Remember to use the correct namespace for the article. For reference, here's the list of the current officially supported namespaces.note If you're not sure which category it is, or if it doesn't seem to fit in any of the categories, you can ask for help in Wiki Talk. Please don't make a new namespace without discussion there first.
Write a brief description At the top of the page, write up a short description of the work. Good things to include: the name of the work's creator(s), the year it was first published, the genre and medium(s), a brief and spoiler-free overview of the plot, and a link to the official website. Things not to include: quality judgements (don't say how much it sucked/how awesome it was), critical reception (that's just a specific variant of quality judgements), recommendations (don't tell us whether or not we should check it out), plot spoilers. And whatever you do, do not copy text from the Wikipedia page. That is Plagiarism and it is bad.
Add a list of tropes At the bottom of the intro, type ---- (four hyphens) to create a horizontal line. Underneath it, create a header that says "!! [Work Name] contains examples of:". (The !! at the beginning of the line is the Header markup.) Underneath that, you're going to make the trope list.
There should be a minimum of three tropes listed (if you're stuck, mentioning e.g. who The Hero and the Big Bad are will give you two tropes right off the bat), or the page is at risk of being sent to the Cut List as a stub. More is preferable, of course, so go through the How to Collect Tropes checklist and write down as many as you can!
Finish off the trope list with another horizontal line: ----.
Once you have a description and a trope list, click "save" to save your edits and create the page. Feel free to use the "preview" feature first to check your work.
Set the page type This step is nice and quick. Go to the "Tools" menu on the left side of the screen. There should be a button that says "set page type". Click on it and set the page type to "work". There you go.
This'll enable things like Reviews and the subpage tabs at the top.
Submit a custom title (not always necessary) This is only necessary if the title includes punctuation; otherwise, skip this step. Under the "Tools" menu on the sidebar, find the "customize title" link and click it. Fill out the form to add punctuation, correct capitalization, and so on. Once a moderator approves it, it'll automatically be applied. More detailed instructions for this step can be found at How to Make a Custom Title.
Cross Wick If you want people to know that your page exists, you'll have to link to it around the Wiki. Remember that trope list you wrote up earlier? Take some time to visit the pages for the tropes you listed and do some Entry Pimping, adding your work as an example on the trope pages. This'll help attract Wiki Magic to make the work's page grow!
Add an image (optional) You can use the Image Uploader to upload an image for the page. Box art or official promotional art (such as a theatrical release poster for a film) is the standard for most media. See How to Pick a Good Image for more info. If you're not sure, you can just skip the image; it looks nice, but it's not required.
And that's it! You're all set. Feel free to click the "add watch" button at the top of the page if you'd like to track changes through your Watchlist.
If you have any questions about this process, don't be shy! Create a query in Ask The Tropers or start a thread in Wiki Talk, and you should get a response pretty quickly. You can also use this page's discussion section.
If you need help writing up a description or coming up with applicable tropes to list, you'll want to find other fans. Try posting in the appropriate Media section in the TV Tropes Forum.
Can I make a page for a work that I created? Yeah, sure, go ahead. You're allowed to trope your own works. Just make sure you understand that once the page is out there, you won't have any control or ownership over it — anyone is allowed to edit it, and any editor will have the same rights and privileges as you. This is why it's a bad idea to make Word Of God statements for your own work on its wiki page.
What if it's not published yet? If your work isn't published yet, you can still make a page for it, but it will have to be in the DarthWiki/ namespace, and it can only be indexed on Unpublished Works.
What if it's a foreign work with a non-English title? TV Tropes is an English-language wiki, so we prefer to use the English titles where applicable. So if the work has an official localized title, use the English title for the page and add the non-English title as a redirect. However, if the work doesn't have an officially-translated English title, you can use the non-English title for the main page and make the English translation into a redirect instead.