I'll be happy to help!:)
1) to stop your feet coming out of the stirrups, push your weight down the back of your leg into your heel, although don't become stiff. That will help a LOT! Heels down, toes up!
2) panicking solves nothing. To steer, sit up, apply rein and keep the horse to the outside with your inside leg. Also, make sure your weight is even or you might be leaning to one side!
3) apply your leg softly, and if they don't listen, use more force. Also, you can't expect a horse to use the corner as much as when you're trotting, so make a small allowance, although still steer round your corners. JAM your inside leg on and push them right out into it.
As for the pulling down the head, give your hands then tug their head back up and hit a small kick. This should really say "NO" to them. Don't let them win!
And for slowing down, don't grip with your thighs. Sit deep, put more weight into your bum and half halt them. Half halting is when you take your outside rein and give a light pull but release it immediately after! This is like a wake up call for them too and can tell a horse you will ask them to do something. If you don't release the rein after, you can face a big fight with the horse, in which they will win.
I hope this helped xx
Custard; I love you! 3/1/2011 ♥