If you're interested in writing for TV, or in making a real, money-earning career out of writing of any kind, then you just have to buy Doctor Who: The Writer's Tale.
It contains a series of emails which Russell T Davies and Benjamin Cook exchanged between February 2007 and April 2008, in which they discuss all things Dr Who: the scripts, the series, the production team and the actors. Fragments of the show's scripts appear throughout along with photos of the show and some of Davies's cartoons, and through this eclectic mix it becomes clear how Davies forms and develops his many ideas, how the Dr Who plots were developed and how the scripts evolved. It's a funny, frank and moving account of Davies's obsession with his work: Davies is a successful writer, but he's become successful through extreme dedication and ridiculous amounts of sustained hard work.
I was going to write a real review of this book, but Keith Topping has already made a much better job of that than I could. So go and read Keith's review here: then go out and buy yourself a copy of The Writer's Tale, because it's a beautiful, rich, and wonderful book whether you're a writer or not.