One of his authors was totally opposed to contractions, and his dialogue never worked. Screenwriters should use slang, contractions, and conversational language. On the other hand, they should avoid writing ethnic dialect because the script may be viewed as politically incorrect. Tiptoe around it. Too much 'on the nose' doesn't give the actor any play. . . .
Timidity is even worse.
You must get to the obligatory pay off. Most movie production companies will not accept a screenplay except through an agent or a lawyer. Many writers have an impossible time obtaining an agent for a screenplay. On the other hand, Paul Lazarus suggests that any writer can hire a lawyer to submit a script. For those who seriously contemplate a screenwriting career, go to Hollywood and expect to wait for 10 years before you see your work on the screen.