One example is: can you get your horse to walk along the outside track, staying absolute straight, on an elastic accepting inside rein contact, with the outside rein continuously like a washing line… i.e. keep the horse straight just with your inside leg aid, not need to use your outside rein AT ALL to keep the horse straight and on the track?
The horse should accept the inside rein contact, with a giving jaw and poll, and NOT misinterpret this contact for a ‘turn inwards’ steering aid…
This is something my very classical dressage trainer asks me to do, and I must admit it led to much embarrassment at times when I realised that my horses couldn’t do it, and that I was sneakily relying on the outside rein to keep them straight and on the track!
Another is to run through, say, a dressage test floor plan, at walk first, then at trot and canter if you are feeling particularly confident, with loose (washing line) reins the whole time – i.e. test whether you can steer and influence your horse accurately with just your seat, legs and shoulder turning aids. You shouldn’t be relying on pulling the inside rein for steering, to be blunt!
If there are jumps dotted around the arena, you can set yourself a test to steer around these, doing loops and circles one way and the other, feeling how much pull the gate to the arena has for example, whether your horse turns more willingly to the left or to the right, if it bends more one way, whether it responds better to a seat or seatbone aid, or to varying leg aids (using thigh, or calf?)
Can you get the horse to turn smartly and in balance across the diagonal with leg/seat aids, rather than using the inside rein?
Can you get the horse to halt purely on seat aids, rather than with the hands?
These are all good fact-finding exercises which are useful to show up the holes in your training and make it easier, in competition environments, to perform smoothly.