A friend of mine does a lot of writing.
If you're not getting published you should consider "why?" if you believe your story is as good as it could be then one answer could be the proposal/pitch you are sending in.
At
http://www.bubblecow.co.uk/ you can find lots of tips for this sort of thing. This friend of mine, while not having had anything published, at least now understands how it should be done!
I wish you luck - do come back and share if you find yourself with a book deal.
All the best,
Spare Ed