One particularly pervasive example appears in the title of this article: the substitution of "ye" for "the". No speaker of early Modern English would do this, as it derives entirely from the fact that the Old English letter "thorn" (Þ) was used to render "th" in writing at the timenote and even then, it had already fallen so far out of favour that "the" was pretty much the only word it was used for, and in some Fonts (especially blackletter), it looked very much like a "y". Since the patent on printing presses was German, and England's earliest printers imported types from the Netherlands, the presses lacked the Anglo-Saxon letter, and "y" was substituted instead. Don't confuse this with the second person plural pronoun "ye," meaning "you," as in "Gather round, ye lads and lassies," which is a different word entirely and is pronounced as written.
Similarly, in the English-speaking world until the early 19th century, the letter "s", at the beginning or middle of a syllable, was written as with the long "s": ſ The character ß (Eszett or sharp "s") in modern German (pronounced and sometimes written "ss") originated as a ligature of ſz. In addition, the integral symbol and the IPA letter esh (representing the "sh" sound) were both derived from the italic version of ſ and look nearly identical note Well, at least in typefaces that have proper italics and not just obliques.
Regarding the second-person singular forms of "be":
For the present, the present indicative is "art", which modern writers generally have no problems with. "Beest" was a subjunctive form that was never used by the King James Bible (it always used "be"), and was used by Shakespeare (who used "be" as well) always with conjunctions that often used the subjunctive.
For the past, "wast" is always used in the indicative (never subjunctive), and "wert" was occasionally used by Shakespeare as the indicative (he generally had it as the subjunctive). The King James Bible strictly reserved "wast" for indicative and "wert" for subjunctive.
Incorrectly following the T-V distinction. "Thou" was informal, and "you" formal, but because "you" later replaced "thou", many modern speakers erroneously think that "thou" is formal. In works such as the King James Bible, however, no such distinction exists; the difference depends on number, not on the status of the speaker and the addressee. So it's not necessarily an error if the author does not follow this distinction; it's an error only if he confuses which pronoun is appropriate, if he does mean to follow the distinction in his work.
Incidentally, Quakers notoriously adopted use of "thee" as a pronoun as part of their tradition of "plainspeaking", in order to make the point that they eschewed all forms of flowery respectful formal speech, even ones that were centuries old and no one thought of as "respectful" anymore like addressing people as "you". The unkind stereotype, of course, is that since they started doing this in the 18th century long after "thou" had passed out of common use they did so incorrectly — "Quaker speech" stereotypically just uses "thee" all the time without regard for nominative or objective case.
"Whence", "thence" and "hence" mean "from where", "from there" and "from here", respectively. Therefore, saying "from whence" is redundant, although it's hard to argue that it's outright wrong since it does have precedent in the works of Shakespeare and the King James Bible.
On that note, "whither", "thither", and "hither" mean "to where", "to there", and "to here", respectively. "Where", "there", and "here" were generally restricted to refer only to location and not goal or source. So "the road there", "the road thither", and "the road thence" mean completely different things.
Some writers seem to think that "thou" can be plural, possibly because they just think it's an older word for "you", and "you" can be plural. In case it needs to be said, "thou" is always singular. "You" can be singular or plural (if the T-V distinction is followed) or exclusively plural (if the King James Bible model is followed, in which case "you" is used as the objective case of "ye").
Getting the cases wrong. "Thou" is the nominative case, "thee" is the objective, and "thy" and "thine" are the possessive. In particularly wretched examples, you may see "thou", "thee", "thy", and "thine" used interchangeably, which is pretty much the second person equivalent of using "I", "me", "my", and "mine" interchangeably. Also, "thyself" was used as the reflexive pronoun.
"Ye" and "you" were used pretty much interchangeably by many writers of Shakespeare's time, with a lot more tendency to use "you" for both nominative and objective cases. But in the King James Bible model, "ye" is only nominative, and "you" only objective. So any writing using archaic language to sound solemn or biblical or perhaps a bit more precise would not mix the two up. Incidentally, the reflexive pronoun would be "yourselves".
Using "mine" and "thine" in front of consonants. They were used in front of vowels, just like how "an" is used today.note "No" and "none" also once worked the same way, the former before consonants, the latter before vowels. By Shakespeare's time, this distinction had died, but one relic of this rule is found in the King James Bible as "none effect".
Only the main verb of the clause is inflected to match the person and number of the subject. So "Dost thou thinkest" is always wrong, since "dost", the main verb, is already conjugated to agree with "thou", the subject; the correct version is "dost thou think"note Grammatically, "think" here is a plain infinitive, which has no ending in Modern English.
Similarly, the imperative mood has no ending and is used as it is in today's English. So "Eateth thy food" is wrong; it should be "eat thy food".
Regarding the imperative mood, for the subject of the verb to be explicitly stated, the pronoun goes after the verb. So "Find the boy" can also be stated as "Find thou the boy" or "Find ye (or "you") the boy" (which pronoun is used depends on whether the imperative is singular or plural).
The pronunciation of the past tense ending "-ed" can be tricky, as it depends on whether the text indicates that the vowel is to be pronounced. You know those "'d" endings you see in some old poetry? There's a good reason for that: it's to indicate that the ending is contracted. For example, "kissed" has two syllables, but "kiss'd" is just one syllable and pronounced as "kisst". Interestingly, the contracted past tense endings became their regular pronunciation in today's English, which is why the original pronunciation of "-ed" trips people upnote Remnants of this pronunciation remain in words like "crooked" or "learned" (as in "learned society"). A grave accent is sometimes used to clarify the pronunciation (e.g., "kissèd").
Verbs in the past indicative ("be" excepted) have the same form for all persons and numbers, except for the second-person singular. The suffix "-est" is used for irregular verbs (e.g., sawest, knewest, tookest) and "-edst" for regular verbs and irregular verbs whose present and past tense forms are the same (e.g., killedst, steppedst, castedst). Special forms include "didst", "hadst", and "wouldst". Thus, "thou loved me" is wrong; it should be "thou lovedst me".
The third-person singular suffix "-eth" works exactly the same way as "-s", in that it is used for only the present indicative. It is not used for the past tense, so such forms as "lovedeth" or "tooketh" are always wrong.
Similarly, the plural of all persons and both present and past tenses has no special ending, just as it does in today's English. There are a few notes of interests, however:
Shakespeare and a few other poets very rarely used "-en" for the plural (e.g., we asken, ye weren). But even then, they meant to sound archaic (Edmund Spenser used it quite frequently in one of his works, but he still meant to sound archaic). The suffix had been much more frequent in Middle English, but by Early Modern English, it had died out.note Ben Jonson noted in his grammar that it had died by King Henry VIII's reign. Incidentally, Jonson complained that it was no longer used, confident that its disuse would be found "a great blemish to our tongue".
Shakespeare sometimes used "-s" (and occasionally with "-eth") with a plural subject, but those uses were seen by later grammarians and modern editors as errors, dialectal or antiquated usage, uses done for the sake of the rhythm or rhyme, or uses done for no adequate explanation (consequently, modern editions of Shakespeare's works erase many of these supposed mistakes wherever they can). For comparison, the King James Bible, quite conservative in its language, reserves "-eth" only for the third-person singular, has no plural ending, and does not use "-s" at all. And if the English grammar written by Ben Jonson, a learned contemporary of Shakespeare's, indicates anything, the correct use for those suffixes lies in only the third-person singular. It's safe to say that "-eth" and "-s" were correctly used only for the third-person singular.
Pronouncing "saith" as "sayeth". "Saith", like "says", sounds quite a bit different from "say", as it is more accurately pronounced as "seth". "Sayeth" was a later invention and is pronounced exactly as it appears. The second-person singular was less consistent (it could be "sayst" or "sayest").
Unlike almost all other auxiliaries, "must" has absolutely no change in form, not even for the second-person singular.note It once did, in Middle English, but the "-est" suffix was discarded probably to make it a monosyllable and thus ease communication.
The past tense of the auxiliary "dare" was "durst" (which incidentally has the same form in the second-person singular, i.e., "thou durst"). "Dared" was not used for that purpose.
Frequently using contractions such as "haven't" or "isn't". It was much more usual to contract the auxiliary with the subject instead of "not" (e.g., "he's not" instead of "he isn't", "I'll not" instead of "I shan't" or "I won't"), and contracting the verb with "not" became more frequent after the mid-17th century, long after Shakespeare's death.
Interrogatives. It was not wrong to say "Where did he see it?", but an absence of "Where saw he it?" would be unusual and distinctively Modern English.note More precisely, an interrogative is formed merely by reversing the order of the subject and the verb; the verb is placed before the subject. e.g., the interrogative of "I know you" would be "Know I you?". In today's English, however, that applies only to auxiliaries, "be", and "have" in the sense of possession, e.g., Have you any money to spare?
Similarly, negatives. It was not wrong to say "I do not know", but an absence of "I know not" would look quite modern.note To negate the main verb of the sentence, simply put "not" after the verb, e.g., the negative of "I love him" would be "I love not him" or "I love him not". But in today's English, that applies only to auxiliaries, "be", and "have" in the sense of possession, e.g., I haven't the foggiest idea.
Misusing "yon". It wasn't just some archaic equivalent for "that"; it indicated something over in the distance. In other words, "yon" suggests that something is much more distant but still noticeable to the speaker than "that" would. More precisely, "this" refers to what is close to the speaker, "that" to what is close to the addressee, and "yon" to what is distant but still noticeable to both (i.e., "over there"). And "yon", "yond", and "yonder" could be used interchangeably as adjectives and adverbs, in case you were wondering. Also, "yon" had no plural form, unlike "this" or "that", so "yon window" and "yon windows" are both correct.
The forms of the subjunctive mood were used where we now use those of another mood or a certain auxiliary of the subjunctive. Many people may unfortunately misread the subjunctive forms as indicative ones or mistakes and miss the intended meaning. It doesn't help that even old writers did not always discriminate between the different forms.
Conditionals and concessive clauses are tricky. "If the hero be guilty" and "if the hero is guilty" mean two different things. The former has the speaker doubt whether the hero is guilty, whereas the latter has the speaker assume the hero's guilt to be true. The same applies for "though he slay men" and "though he slays men" (except this time the time of the verb with the subjunctive form is either present or future, and "though" there really means "even if"). The subjunctive shows doubt, and the indicative shows actuality or reality.
For time clauses, the subjunctive form is used because the subordinate verb has not occurred in relation to the verb in the main clause (e.g., "Leave before my master find thee").
For purpose clauses, the subjunctive form is used because the speaker means to indicate desire (e.g., "Gather everything in order that nothing be lost", "See to it that they be given the treasure"). Even today, we use the subjunctive form for "lest" clauses (e.g., "Leave lest he catch you").
A bit less obvious, but expressions such as "be it enacted" or "God bless America" are really subjunctives, which is made clearer since the verbs are not inflected for the third-person singular in those phrases. They really are archaic ways to say "let it be enacted" (imperative in form) and "May God bless America".
The main clause of unreal conditionals might not use the subjunctive form you're used to seeing. "It were foolish to do that if I were in his shoes" really means "It would be foolish to do that if I were in his shoes". And "if it had not rained, he had arrived there" really means "if it had not rained, he would have arrived there". In fact, the more extensive use of the simple past subjunctive form is where expressions such as "had rather" ("would rather" appeared later) or "had better" come from.note An identical sentence structure for those conditionals is used in German, in which language it is much more obvious that the verbs in both the condition clause and the main clause are subjunctives.
Elizabethan English contracts many words that we don't contract today. For instance, "e'en" for "even", "th'" for "the", "'t" for "it", and "o'er" for "over". Many old poems even treat "heaven" as a monosyllable, awkward though it may seem.
The past tense forms of several irregular verbs are not necessarily the same as those we use today. For instance, "brake" might be used for "broke", "gat" for "got", and "spake" for "spoke". Also, some irregular verbs of today seemed to be regular verbs back then. For instance, "builded" for "built" and "digged" for "dug". And some regular verbs of today seemed to be irregular verbs back then. For instance, "clomb" for "climbed", and "holp" for "helped".
Technically, the possessive form of the neuter pronoun "it" was not "its" but "his" (this non-personifying use can be found in Old English). This can be seen in "if the salt have lost his savour" from the King James Bible. Other alternatives used by the Elizabethans were plain "it" and "thereof" (e.g., "this text and the author thereof"). So if you really want to be historically faithful, using "its" for an Elizabethan's dialogue will not be right. That said, this hasn't stopped modern editions of Shakespeare's works from using "its", so using "its" in archaic-sounding dialogue or text may not be seen as a mistake even by those who know better.