I really did not know if I needed a script. I have never like writing, until lately. I thought “ As long as you can keep the script on your head, you really don't need to go trough the whole writing process”. But after several failed attempts of making a non script production I decided to learn to write.
I read The Screenwriter's Bible by David Trottier I recommended, it help me so much.
I also read a couple of script of my favorites movies, as Pulp fiction, Decostructing Harry and Pay It Forward. You can get transcripts and scripts here http://www.simplyscripts.com
I join the trigger street community, where you download scripts and shorts of aspiring filmmakers to review, some of them are amazing, some are not so good, but you learn from both, and more important, you can see what other people are writing about, and the different style they are using.
