V poles help encourage the horse to pick his feet up!
Do some slightly raised trot/lope/canter poles to get him to pick up his feet
I agree with what Taylor has suggested but also take a look at yourself. One of the most common mistakes from a horse is due to us! Try sitting back and really lifting your horse onto his haunches (of course not over exaggeratedly) then try the grid work which will help tremendously but always remember to fix yourself before looking at the horse :)
Grid work, pole work, cavaletti work, etc. it encourages the horse to lift his legs:)
Try smaller fences in the trot so he doesn't run through the bit, if that's doesn't work go back to poles for a lesson or two and work on slowing him down in the canter or trot over them and apply that to your jumping :) good luck
Try a cue before a fence, i light heel tap, or strong leg pressure. I rode a horse that i had to literally run my heels up her side to get her to pick her feet up.
I would try poles before and/or after the fence :)
More cavaletti work. And if he's young, he will be better just give he time.
I'd recommend a lot of pole work and grid work to help him become more aware of where his feet are. Ground poles and stride poles also help them judge if they're struggling to see it.
I had a horse that just got really cheeky when she realised our poles were plastic and could knock easily, so we swapped our top rails for lead poles. Hope this helps!