- practice two point position without hands
- make sure you are pressing your weight down into your heels and not pinching with your knee
- have even pressure everywhere on your inner leg.
- practice posting without hands.
- try double posting (post in the rhythm of up up down, up up down).
- practice riding without stirrups.
- practice not only two point, but also vertical position (standing almost straight up, really open hip angle) and superman position (a really low two point, stretching your hands toward the ears and your hips out behind you) make sure you always keep your heels underneath you, don't let them slip behind you. do this without hands first standing still, then work up to walk and trot and canter.
good luck! if you really want excersises specific to your faults, send a picture.