Originally Posted by Lexiie
Also, I squeeze as hard as I can with my calves when posting. I notice when my leg moves so I keep squeezing until i'm still.
Please, don't do this unless you want a horse that is completely dead to all leg aids. You can't have subtle aids if you're already squeezing as hard as you can with your legs in the first place. Also doing this could potentially create a sour horse in the long run, because having someone grip with their legs as hard as they can is not all that comfortable for them.
I do however like the suggestion of posting up for two or three and down for one. It's great for the core, leg, and overall balance. Also practice standing up in the saddle and trotting, keeping that position for as long as possible. Do some no reins jumping over cavaletti or tiny little x's and poles. No stirrups work is great but make sure not to grip with your knees. Practice steering more with your legs and seat, less with your reins.
Also make sure you are riding on a regular basis. It takes constant riding to build up that leg muscle, and having long periods of time between every time you ride can really set you back. Even putting few weeks between every time you ride will make it near impossible to keep a nice amount of leg strength. I've been riding weekly for almost 6 years and I have relatively strong legs but if I take a few weeks off, when I get back on my legs will be sore and weak. You'll never be able to maintain that muscle without constant riding.
May I ask how often you ride, exactly how long you've been riding and how much you are about to do?