Work on no stirrup work because it really engages your leg muscles as you’re trying not to fall off. Two point also works wonders!!
I would recommend lots of heels down work. It really stretches you're hamstrings, and running sorta helps you're legs too. Hope this helps!🙃
Work on lots of two pointing and posting trot without stirrups!! It works wonders! Also try popping over some small jumps (cross rails or short verticals) without stirrups! Hope I helped!!