Secondly, there are lots of magazines and publications on screenwriting that you can read. Thirdly, I'd take my best script and submit it to film festivals and other screenwriting competitions. This will help his career. You write excellent, off-beat characters. Writing good characters comes from observation.
People are fascinating.
They're full of great wisdom, contradictions and big surprises. I like to take a character who seems pretty obvious to the audience and then show some aspect of him that you'd never expect. Sure, he's a big, bad biker, for example, but he knows the names of all the flowers and trees, or he reads poetry. Give a character that depth by finding what isn't obvious about him or her. Sure, she's a bitch, but she always holds the door for people.