Alright...first things first. Place the ball on the side of your head, where it is most comfortable. Not on your temple....people that side headstall here look bad.....it should be around your ear, or just before it. When the ball is on your side, you should be able to look straight ahead, and your head should be parallel to the ground.
Once you are able to balance the ball successfully by placing it there with your hands, practise the move from headstall. To do this, you have to move into it fast. Feel the ball move onto the side of your head, dont rush it, but dont take your time.
The next step is to get side headstall from foot stall, this takes ALOT of practise. Dont give up though, cuz its not impossible. You should probably practise this first by throwing it with your hands, rather than your foot....wateva suits. When the ball is in the air, pretend to headstall it while its in air and close to your head, than quickly go to sideheadstall when it lands. This is hard to explain but you should get what im saying after practising it.
Good luck with it :cheers: