A great exercise for improving lateral suppleness and enhancing the quality and discipline of your lateral work:
On the right rein in walk or trot ride leg yield from M to the three-quarter line. Change to riding shoulder-in left along the three-quarter line, then half-pass left to F. The bend is to the left throughout the exercise. Obviously this can be repeated from F to M on the left rein with the bend to the right. The hardest part is preventing the quarters from swinging out in the shoulder-in.