Draw reins. Some will say that they are only because the rider is to lazy to make their horse work but really it teaches them how to
Lunging in the Pessoa training system.
Always always strech trot both directions after your ride. Also, draw reins!!
My trainer has us work on hills in the field while letting our horses stretch their necks down as much as the want
Lunging with sidereins
Practicing stretching forward and down on and off of them all 3 gates
Going over poles while your horse is on the bit and round (it will only hurt them if they are not correctly round)