You'll save a lot of time if you choose your books several months in advance.
Some groups have a meeting once a year just to choose books for the coming year.
Others choose six months worth of books at a time. Try choosing your reading group books with a theme in mind. If you choose books several months at a time, you can think about ways to tie your books together. Discussions then include comparisons among all the books you've all read, and are often more satisfying. The downside of this last theme is that it involves a lot of research by the book choosers.