Easley Blackwood, Jr., pianist and composer, was my instructor for an independent study course in composition when I was in college. He once told me that there were two ways to approach any art: one was having made as full a study as possible of all of the details, including what others in the field have done; the second was naively, leaving one free of influence, but also free of what might turn out to be essential knowledge.
If you're writing the kind of book for which there is competition, at some point, you need to both analyze the genre and also see what your competitors are up to in order to speak to this point in your book proposal.
The need to look at everyone else's approach may make you feel that it's difficult to be original. I approach this by following this sequence:
1) I do an initial plan of my book before looking at the competition, keeping influence at bay as much as possible.
2) I read reviews of my competition, both using Amazon's review feature to see what customers are saying and using JSTOR through the UVM library's online resources to see professional reviews. This usually brings to light several things that could use improvement, and I incorporate these into my plan as they fit. I also note what they were praised for and consider what I can do in this regard (without plagiarizing).
3) I read the closest competitors and make notes on my experience of the book as a reader. This also brings up new ideas - both about what was well done and also what I can do better.
By starting my plan before looking at how others approached it, I am able to think about the book's subject "outside the box" and without conventional tethers. Examining the competition and what others think of it then builds on that foundation—altering it, if necessary, to fit any genre conventions or reader expectations about which I may have initially been unaware or just forgotten to address.
Of course, each book proposal is different, and sometimes book ideas come about when you're reading a book that suddenly turns—by the bubbling up of the idea—from your leisure reading into competition in an instant. But still, the sequence of sketching out your ideas before purposefully researching the field may help you create a proposal with a more satisfying blend of expected generic conventions and original elements.