Where to start the story? What the story is really about? Length – too long, too short? What your protagonist wants? Multiple points of view? Structure? Anything having to do with marketing, pitching, querying? Holding yourself accountable? Finding time to write? Doubting whether it's any good?
Remember that we have no clue whatsoever. Help us see your book on the shelf. Pretend you are writing copy for the book jacket — entice a reader by explaining what the book is about, but also get at why the reader might care. For examples, check out the write-ups for books on Amazon.com, or pull a book off your shelf and read the description, found either on the back (paperback) or the inside cover flap (hardback).