In general I have to both love a book and to think readers of my work could reasonably be expected to like it, too. By "like" I mean resonate to the mood, tone, pace, and/or prose of the book. I honestly don't give a shit about subject matter/genre: a good book is a good book. "Love" means like, admire, want to read again. "Love" means getting some kind of charge from reading it. "Love" means desperately wanting others to read it. Few books hit that standard for me.
The odds are, then, that if I do agree to read your book with a view to blurbing, I'll end up saying no.
If you want to try, anyway, I'll need to read either an ARC (mail to PO Box 77361, Seattle WA 98177) or Kindle format, plus all the usual info: publisher, price, date, agent, etc.