Of course you know that it takes practise, there is no magic trick in getting a trick, the key item in freestyle is practise
But in headstall, what you want to do is have the ball balanced right on your hairline like where it starts, you shouldnt have your neck far back or to far forward, just look up. Alot of ppl headstall right on their forehead, and lottappl nosestall when they headstall, looks really uncomfortable and looks shit imo. So place the ball on your hair line with your hands and balance for aslong as possible, keep on doing this until you can headstall, then you can try foot to head............once again, practise practise practise