They will be sure that the photo is well lit (my biggest beef with amateur shots), and that the subject is well composed, etc.
Beyond that, show us your personality, pose in those fashions you consider sexy. You don't have to spread your legs, but it's always nice to see a little skin.
Finally, if you don't want to show your face, that is understandable, but don't just put a blue dot over it or blur it to the point of ridiculousness. Instead use your hair if it is long enough to obscure your face, turn away from the camera or shoot from the neck down.