Screenwriter/blogger Bryan ‘Locke’ Naegele speaks the truth: it’s just as important to read bad writing as good.
The first reason to read bad scripts is to constantly expose yourself to what doesn’t work. Don’t learn from your own mistakes, learn from others. That’s my motto. That way yours are much more manageable because they’re fewer. You become hyper-aware of flat characters, shotty dialogue, predictability, clichés, etc.
I assume “shotty” is a cross between “shoddy” and “shitty.” I like it.
I worked as an intern-slash-reader at a little Paramount production company during my first semester of graduate school, and the contrast between the crappy scripts I read there and the great scripts I read for class was really illuminating. And encouraging on some level. I knew I could never write as well as Lawrence Kasdan, but I could easily write better than the schmucks I had to write coverage on.
So, take Bryan at his word.