Most of the time this is accomplished with a forward or backward roll. This provides vestibular stimulation as well as tactile contact with the mat. Regular ukemi practice also provides students with a kind of emotional resilience. They learn that they can fall and not necessarily get hurt and bounce up again. Students getting up from the ground from a roll essentially push themselves up, providing themselves with proprioceptive stimulation to the shoulders, hips and knees.
Students learn joint locks to immobilize their partners, getting further proprioceptive input.
Most of the techniques are done in a kneeling position as well as standing. This is taught for the very functional reason that, until recently, kneeling was the way Japanese sat in their homes. They were expected to be able to employ self-defense techniques in whatever position they were likely to spend any length of time. The suwari waza position, halfway between kneeling flat with the feet tucked under and tall kneeling, is an excellent one to develop trunk control and balance. Students learn to move with their partners and be sensitive to their movements.