In my happy, naive days, I thought all you had to do to get a book published is write a lovely, well crafted, entertaining manuscript. You would send it off to a publisher, and they would carefully consider it before - promptly - informing you whether they would like to take it or not.
Those were the days. Now I realise knowledge of the publishing business is crucial. When I was studying the MA we had a module called 'Publishing Project' and we had a number of speakers visit, who talked about their experience of the industry. What an eye opener. I know a few fellow students were very disheartened (they probably cherished beliefs a bit like mine) and talked about giving up.
But a very good book was recommended to me. Carole Blake's From Pitch to Publication, while out of date in some respects, is a real how-to in others. There's a fabulous interview with her at Gemma Noon's blog, The Literary Project.
Betsy Lerner's The Forest for the Trees is also useful, even though focused on the American market, many issues are the same.
Knowledge of how to sell your work is invaluable. You get one moment to impress, and it's worth spending time working on your 'elevator pitch', your query letter and your synopsis. Of course, this is only important if you've really written (and rewritten, and edited) your masterpiece. Ultimately, the above are all aimed at impressing someone enough to give your book a shot. That, then, has to impress.
So, I think it's worth spending a little time acquainting yourself with the world you are trying to get involved with.