Touch, praise, treat, touch, praise, treat, repeat repeat repeat repeat!
I could barely touch my big girls back legs without her dancing around at first. She wasn't as bad with her fronts, took lots of patients and lots of praise, but she now lifts them just by touching her heal. She does so well, I am teaching her how to extend her front leg up and out to shake on command.
Wanted to ad that any amount of positive behavior deserves praise. Even if that is only a touch at first, then even if you work towards getting her heel off the ground, then the hoof an inch off the ground, any amount of give on her part is an advancement towards your goal and deserves praise, even if that comes in the form of release of pressure (whether it is the mental pressure of stopping and allowing her to relax when she has behaved positively towards your actions of touching her or it may be the actual physical pressure of you getting her foot off the ground an inch, then two, and so on when she gets to that point.). Stopping and allowing your horse to know that they have done what you have asked and walking away, even if it is only for ten minutes is a huge deal, if you don't want to walk away altogether, move onto brushing or leading them around, then come back to there legs again.