I have done the first two exercises, and I must say they help a LOT! I would also suggest riding bareback, at the walk and trot (canter only when you are balanced and relaxed at the trot). While riding bareback, doing some posting and 2-point can help build strength in your thighs and lower back. Be careful not to pinch with your knees or do any other "bad habit things". When your horse is saddled, try this exercise: Stand up in your stirrups. It is harder than it sounds! Although you will need to rely on your stirrups for this exercise (against the rule that you are supposed to rely on your thighs and seat) it will, however, help improve balance and help you figgure out the correct leg and foot position. Once you find your balance (not falling over the horse's shoulder or falling back into the saddle), sink slowly into the saddle without changing your leg or foot positions. It may feel wrong the first few times if you were used to an incorrect leg position, but if someone were to take a picture of your "new" position, your ear, shoulder, hip and heel should now be aligned. I still use this exercise a lot, especally when trotting.