Several books and articles exist on the different “rules”, facets, and principals of screenwriting. However, in the end they all seem to cover similar ground. Here are some basics I’ve collected. This is by no means a comprehensive list. It would be impossible for something as broad as screenwriting to ever be boiled down to only three points. These are just common themes of advice.
Don’t be boring
This is probably the most important thing in screenwriting. It stands for any other type of writing as well. There are all kinds of principals and guidelines given on how to make a good screenplay. A lot of them boil down to the same thing: don’t be boring.
Lots of the little “rules” like don’t write monologues, or do flashbacks or voiceovers are proven wrong by popular movies. The Godfather opens with a monologue. Anyone whose seen Fear and Loathing in Las Vegas knows how hilarious those can be. The show “Lost” is built off flashbacks. These rules are intended to help the writer not be boring because these things are so easily done wrong. Thus it’s not that a writer shouldn’t use monologues, flashbacks, or voice-overs. It’s that they shouldn’t write boring, stupid, or otherwise retarded monologues, flashbacks, or voice-overs.
It’s obvious why you wouldn’t want to be boring. If you bore your audience they will wander away. That’s bad if you ever expect to get paid. It’s called the entertainment business for a reason.
You can only confuse people for so long
You can’t drag your audience along for two hours, or for several seasons, without answering at least a few questions. You’ll make them angry and they will wander away. See the point above for why wandering away is bad.
You still don’t want to give everything away in the exposition, as this will make a boring movie. How much information to unravel, when and where, is an instinct most people develop through practice. However, it’s a good idea to keep the set up of the story short and sweet in proportion to how long the work is going to eventually become. Tell things along the way, and make sure all the important questions are answered by the final fade out.
Stay away from clichés -be innovative
This idea is also pretty standard in screenwriting advice. The reason to avoid clichés is because they are one-dimensional and over used. Thus why the name cliché has such negative connotations. Clichés are boring. This doesn’t mean you can’t take a cliché and throw a twist to it. However, once you put the twist on it, it’s no longer a cliché and thus you no longer have reason to worry.