More Slogans...

Screenplays come in three sizes: Long, Too Long and Much Too Long.

Exposition is BORING unless it is in the context of some present dramatic tension or crisis.  So start with an action that creates tension, then provide the exposition in terms of the present developments.

PASSIVITY is a capital crime in drama.

'Comedy is hard' (last words of Edmund Kean).  Comedy plays out best in the master-shot.  Comic structure is simply dramatic structure but MORE SO: neater, shorter, faster.  Don't attempt comedy until you are really expert in structuring dramatic material.