As usual, I'm the last to post this, but hey, better late than never, that's what I reckon. So you'll all know this already, but just in case you don't: Adrian Mead has written a book about getting your screenwriting career started. It's called Making It As A Screenwriter, it's £7.79 (about 9 quid including VAT), available from here, and all profits go to Childline.
Now, you all probably know I'm not a fan of screenwriting books. Things that tell you how to write, and waffle on about inciting incidents and third act reversals and all that bollocks, aren't worth your time or money. But this one doesn't tell you how to write, it assumes that you can write, that you have some talent. It tells you the things you need to know to break in - getting an agent, approaching companies, how many scripts you need, what a treatment is, re-writing, feedback, all that good stuff. Simple, straightforward advice from a professional writer.
If you're just starting out, or fairly new, then you need to read this - it'll save you a LOT of time. And even if you're an old hand, you'll probably learn a thing or two, or even just be inspired to get off your arse and do some work. I'm one of the many, many people who have given testimonials about how good the book is, so go and pick up a copy. It's for a good cause, and it will help you out. Everybody wins.
Note: It's based around the UK industry, just so you know - but a lot of the advice applies anywhere.