Hopefully every writer knows that the most important sentence in your book is the FIRST one. And that criticality applies to the first paragraph and first page, also. You will gain or lose a potential reader/purchaser based on the first few lines of page one. If you don't grab them with that, they will likely not buy your book.
So we'll be having a couple of blog posts on this topic in a few weeks. As part of that, we will critique some "first paragraphs" sent to us. If you'd like our advice, send the first paragraph (one paragraph only, whatever length you have) to email@example.com by March 3, and we'll select as many as possible to dissect here.