Have it be a naked pic. The hottest part is just around the goodies, so if he's wearing underwear and there's a book nearby, why bother? Also, show his face. It's always nicer when they're cute and not a poorly cropped torso. Make sure to cover all of the bits, and not leave anything poking out. And don't forget that all of my readers are horny bastards and will recognize the latest 'model' from Sean Cody, so have it be a random pic of a guy not in a porno. It could even be yourself, if you're so inclined. No one will tell.
Here. Let me give you a few examples.
A Thousand Splendid Suns by Khaled Hosseini

The Master by Colm Toibin

Handling Sin by Michael Malone

The Thirteenth Tale by Diane Setterfield

The Good Terrorist by Doris Lessing

Email me (link in sidebar) or leave a comment with the url of your selection into the Raw Youth book club. Or whatever.