I mentioned this in the comments to Suckerman's post about Heinlein...
Brian K. Vaughan (Lost, Y the Last Man) wrote a nice piece on establishing yourself as a writer. The piece isn't very long, but here's my favorite bit:
WRITE MORE, DO OTHER STUFF LESS.
That's it. Everything else is meaningless. You can take all the classes in the world and read every book on the craft out there, but at the end of the day, writing is sorta like dieting. There are plenty of stupid fads out there and charlatans promising quick fixes, but if you want to lose weight, you have to exercise more and eat less. Period. Every writer has 10,000 pages of shit in them, and the only way your writing is going to be any good at all is to work hard and hit 10,001.
I've always admired Vaughan's writing, and not just because he has a very similar background to many of the members here in the Screenwriters League.
On an unrelated note, the AVClub has a great breakdown of movies the turn their audience into voyeurs. Definitely a good read.