Main IdeaBefore you can write a Korean Drama, you have to understand what makes it a Korean Drama (Besides from being Korean, but that doesn't count.) Korean Dramas are usually aimed at the female audience, and focus mainly on themes such as romance and family. Expect to use the Asian value of filial piety and respect for seniors which is prevalent in Korean culture. A lot.
Necessary TropesThe protagonist is always, and will always, be female when it comes to Korean dramas. The heroine is usually a Plucky Girl, Genki Girl or Pollyanna who will possess tons of determination for her to survive the plot. Take note that the audience needs to sympathize with her, so the character should not be overly annoying or clingy, that role is reserved for the resident bimbo or love rival. Make sure the Heroine Will Not Be A Victim when life throws her pitfalls, or make her an Action Girl, give her some spunk, clumsiness, (for comic relief) or snark. Do not make her a Damsel in Distress. Even though some dramas have gotten away with it, and dramas always have some Damsel in Distress moments, it shows that the heroine is unable to take charge of her life and is always dependent on the males. In the female-empowered 21st century, she will lose interest fast. Remember, the prime target of these dramas are females. Korean dramas always have two or more love interests. The Main Love Interest will usually be a Jerk with a Heart of Gold Lonely Rich Kid, because All Girls Want Bad Boys. Why is he that way? Maybe he's plain spoilt with adoring parents and swooning "friends" and needs an ordinary girl to stand up to him, maybe he has been starved of love because he has a Dark and Troubled Past with Parental Abandonment, or he's just trying to maintain that Jerkass Fašade in front of his perfect and unreasonably demanding parents. A main part of the romance is discovering the Hidden Heart of Gold part of the Jerk, now that he is able to see the brighter side of life and the good in people thanks to his new heroine girlfriend. The other love interest is usually the Nice Guy and/or Dogged Nice Guy with a Big Brother Instinct to the heroine. He's the guy who will lend her a shoulder to cry on, give her a helping hand in life or tell her the right thing to do when problems arise. The heroine might think that they are Just Friends, or that they have a Like Brother and Sister relationship, not knowing that he wants to be more than that with her. Unfortunately, his efforts are usually unrequited, because Nice Guys Finish Last, but he will be selfless enough to recognize that the heroine really loves someone else, and will give her up. Other potential Love Interests are usually a playboy, a dream guy who turns out to be not so perfect after all. Sometimes these tropes are instead infused with the two main love interests. Here is something very important about eligible love interests, no matter what personality or moral standing, they must all consist of 1000% Mr. Fanservice. The Big Bad of the series is usually female, it could be the scheming stepmother or vicious mother-in-law waiting to seize power or money or both, it could be love rival watching out in case the heroine gets her man, because Love Makes You Evil, and she will attempt to seduce the main love interest or get rid of any love rivals. If the two girls are related in any way, such as step-siblings, expect them to possibly be Betty and Veronica types. Sometimes there are two antagonists, both the scheming ambitious middle-aged woman who is using her daughter the love rival to capture the heart of the male love interest so that when he inherits the multi-million dollar empire his family has built, all the money will go to them. Subversions and other versions exist, but the Big Bad is usually motivated by ambition or money or love, and they do not need to be necessarily female. Please remember that these tropes describe a conventional Korean drama as a typical Romantic Comedy. Not all Korean dramas abide rigidly to these rules, although you can always find shades of these in them.
Scene StagingBad things always happen on the banks of the Han River. You want a couple to break up, someone to get assaulted, tell your lover you have an incurable disease, etc., etc., it must be done there. Preferably at night by a beautifully-illuminated bridge. In order to prove you are in Seoul, at least one major scene must be in and/or around Namsan Tower. A hospital stay will always involve having an IV attached to the patient (so they can Pull the I.V.), and a humidifier by the patient's head.