Grids, bounces, gymnastics and wide jumps with fillers. (Oxer etc) or any type of jump that will make them think about what they are doing. I know a lot of horses that will trip over small jumps, but jump 4 ft+ with ease.
I like to build out the fill of a jump so its wider for the horse to jump over, so its kind of like an oxer
I do grid work so do a bounce then 1 stride then 2 stride and it really helps the horse concentrate on their technique!
on top of what everybody else has said, try v-poles , they help with overall technique.
I took my horse hacking and had her jump solid objects (fallen tree limbs and such). The objects were a reasonable height, but obviously didn't move or fall like show jumps so gave quite a shock if she got lazy with her feet and knocked into the tree. Now, she is extremely careful and leaves a good bit of space between her and any jump she comes across.Hope that helps!
Bounces, gymnastics, cavelettis, pole work, and transitions within the trot and canter (extended, working, collected)