I taught myself how to read and analyse screenplays when I started out running this film festival, Between 1992 and 2003 I read and wrote critiques on over 2,500 screenplays including Lock, Stock and Two Smoking Barrels, and 51st State.
Only a handful of these 2,500 screenplays ever got made. Of the remaining scripts, they most likely will never get made, and not because they were a bad idea for a screenplay. I never once found a bad idea for a screenplay reading 2,500 scripts. did find poor execution of the ideas time and time again.
I'm no expert. All I have is a body of experience working with rookie writers. Here is a crib sheet of the basic mistakes debut screenwriters make.
Read 7 Mistakes Rookie Screenwriters Make