So, I'm writing a screenplay that has a bunch of genres in it, drama, war, teen. And I know that it's going to have some comedy in it, from sarcasim to plain out jokes. But how do make sure that it's appropreate for the scene and isn't totally out of place? Or how do I make sure that it smoothly fits in with what going on without crushing the whole mood.

The best thing I can suggest is, make it sound natural. If you cant read it without hearing a rim shot, you know you're in trouble.

Listen to the conversations of those around you: punch lines emerge pretty much organically. You should strive for that as well.

I add punchlines by just making them part of the conversation. Like in one scene of mine, they are discussing who reads the dictionary. They make fun of one of my characters for only reading the thesaurus, and I just mad the dialogue around the joke. Or put in a parenthetical saying (getting back to the topic) or an action saying They laugh, but then realize they have a topic to attend to.

That's what I have. It's all in getting back to the dialogue after the joke.

I actually think that punchlines should be avoided in scripts and that the comedy should come from the situations/conversations themselves. Since you're not doing a straight-up comedy though...I'd give your characters quick witty lines to say, since that's more natural than jokes-in-conversation (think one-liners in The Mummy or the Die Hard movies).

Also..re-read them after your wrote them with a friend or something. it'll really help with determining whether or not its out of place

Punch-Lines, as said above, shouldn't really be present, unless it's a form of set-up for some other joke, like an off-handed comment about it. Conversations flow naturally, and so should your script. I'm writing a Comedy too this year, and it's going to be somewhat physical, and rely more on the differences in characters to draw out the comedic effect. One great playwright to look at for inspiration is Neil Simon. His plays flow very nicely and are amazingly funny.

Shakespeare always liked to pop a comedic character into his tragedies... usually a fool who, though less educated than everyone else, had more wisdom. He wasn't above poop jokes, penis jokes, and the occasional punch line, either. Just a thought- maybe you can use a fool?

I mean, can't we all? ;)

Break a leg!