First and foremost for men, photos of your bare chest (whether it buff, hairy or not) are not cool. Save it for someone that wants to see that. A photo of you dressed in a nice dress shirt (with just you in the photo) with a great smile looking into the camera would be far sexier.
Women you too need to have a great photo and a current one at that. Don't post a photo of you from twenty years ago when you thought you looked the best. You want people to recognize you and know who you really are. You too should have a photo taken in a soft colored shirt or sweater (keep it simple no prints) looking at the camer smiling.
Have a photo taken by a loved one every year to keep your profile pictures updated and looking like you.