Here's a great little youtube clip with some fantastic words of advice for anyone trying to break in as a screenwriter. The bit at the end from Bruce Joel Rubin is especially worth hearing. The unanimous verdict?
Commitment is everything. Making sure you're all in is the only way to survive the 10 or more years of persistence it takes. Buckle up, and get typing. Have a watch:
Also, here's the link to John August's blog full of info and insight. Have a look: johnaugust.com
Hope you found this helpful.