This is easier for women than men. Many of Facebook's most interesting women have learned long ago that a photo framed with 20 percent face and 80 percent cleavage is often ideal. What do you do if you're a guy? Even if you're pecs are some of the best in the game, they likely aren't going to titillate Facebook friends enough to earn you a poke, let alone a thirsty private message. The best course of action here is to experiment. Maybe you can flex hard enough to make it look like you have a six-pack. Perhaps a close-up of your bicep will make it look like more than a product of three sets of 15 pound weights and masturbation. Selfies are like vain, pathetic snowflakes: there are infinite angles from which they can be taken. Spend an evening photographing every part of your body from every imaginable angle and you are bound to find something attractive eventually.
Emphasize the most appealing parts of your body.