Have you ever been really, really, really hungry? Have you ever stayed awake for 48 hours in a row? Did you break a bone? Did you fall in love...or fall out of it? Well, why don't you write it?
Life Experience
When you're a writer, you're going to hear the phrase life experience a lot. But you don't have to go to Italy or kill a guy in order to get life experience. Everything you've ever been through, no matter how seemingly mundane it is, can help you write a book. If you've felt hunger, if you've worked out until your muscles ached, if you've smelled the perfumed scent of a cigar -- all of it, any of it, can lend rich details to your book. And the other stuff that you haven't done? Well...you can use research for that.