I don't send out photos for sexts, because I'm very paranoid about digital media, but I do have some experience hailing from the days of "let's-nick-my-dad's-polaroid-and-exchange-pictures, tee hee". And I we still have the pictures. Mwahahaha, naked young boyfriend pictures. Ah, nostalgia.
Tips:
Set the camera down the camera, use autorelease. Shots come out much better if you don't have to drape your body around the arm holding your phone.
Don't just make your pictures "BAM, HERE CUNT, IN YOUR FACE, GO!". Play with his gaze. Lead him to where you want him to look - with a gaze, with a pointed finger, with an arm, with a lifted leg...
...and closely connected to that, tell a little story. Make it a frame frozen in time.
Play with a setting. Not a setting on the camera, but in the picture. Put a little mood into it.
His favorite "sexy polaroids" of me? You'll find much of the above worked into them