Short of hiring a small volunteer staff to read through and review those novels I'm simply unable to, it takes a name that I recognise, a synopsis that really gets me going or else a publisher or imprint that I have the utmost confidence in to ensure that I'll make the time to read something.
Any of those things - or, I find today, some truly kick-ass presentation.
Because once in a while, a book isn't just a book. Someone goes the extra mile to grab my attention. They slip a CD of recommended music to read by inside the front dustcover - as with The Whisperers by John Connolly; they'll write a letter explaining why they think this book, over all the other books, is worth my attention - many Gollancz releases do this; or bind a printed manuscript for me to read before nigh-on everyone else - see the great Kraken and Neil Gaiman's collection of Stories.