I'd probably suggest making sure there's some common ground. I'm guessing you visit the bookstore often and therefore read a lot yourself... Look out for a woman looking at similar titles. If she picks a book up that you've read, that could be your "in" to speak to her. Comment on the book, say whether you thought it was good work or not, then smile snd be approachable. Ask if she's read that author often, see where the conversation goes. Most importantly don't place too much pressure on the conversation going somewhere - a lot of conversations end abruptly and it's quite usual in this day and age. It's not because you're not interesting, etc, people aren't very trusting of strangers and some may have their reasons for not wanting to talk. But as long as you're friendly and approachable, one day you'll just click with someone and it will happen naturally