So you can practice on a chair stretching down to your heels, practice raising yourself off the chair as if posting on the trot. You can lay in bed and stretch to your heels. Or raise legs off ground straight out and up. Or raise legs straight and up a little then bring them into your body then out straight without touching ground. Or you can do calf raises by putting weight to your toes and raising yourself up. It helps with calf muscles. The leg raises help with the inner thighs. Practice sitting in the chair with a straight back but not stiff and with your butt NOT sticking out, keep your shoulders straight not tight and sit tall and proud.
You can even when on the horse do bare back riding so that you can precise the skill of legs. Do walk trot and canter. Take your time. Canter is easier than trot: not as much muscle used. Even when in saddle be sure to always be aware of your legs. You can even practice just riding with your leg pressure. NO REINS! Or a little if anything. Or practice with out stir ups. It is easier to do with english saddle since leathers and irons come off. IT TRULY HELPS
! And when you feel ready have someone watch you and make sure your legs don't move crazily, i'm just getting out of that stage! HEHE! But just keep practicing on and off and be sure to stay positive and if you get frustrated get off the horse or just walk the horse. Just please remember to use a helmet, you never know what could happen, even on the best horse something could go wrong and you could die, be careful and happy trails!!