Consistency

Within each gait, consistently ask for transitions from collected to extended, both straight and in lateral work. Remember to keep the contact consistent by flexions left and right, changing the bend, keeping the horse supple through a thousand transitions of shoulder in, renvers (choose wisely in canter- ride renvers in canter infrequently only when asking for inward spirals and canter to walk transitions, always remember to straighten the canter), travers, leg yield, half pass in every gait (full pass in walk). After our initial stretching warm up, it's time to expect both Delphi and me to consistently perform: me by leading with my pelvis in front of my shoulders, keeping my legs back for collection, keeping the frontal plane parallel to the direction I want to move, and requiring a supple contact through all gaits and transitions; Delphi by learning through repetition that she is now required to be through and supple in all work.
An exercise that encourages all of the above:
In canter, ride a square where you make a deliberate quarter pirouette at each corner. In the turn maintain the slight inside bend with your inside leg and rein, and put your outside leg back and think "haunches in" and allow the turn to make the beginning of a canter pirouette. Then ride absolutely straight to the next corner and repeat. Use counter flexions as needed to maintain straightness, suppleness, and throughness.

To improve the photo: the shoulder plumb line should be behind the hip joint, every down beat the hips are sent forward in the direction of the horse's travel, so you can afford to "lean back," maintain tone/elasticity by springing on a trampoline rather than just flopping down onto the horse's back:
To improve the photo: for canter the two points of stability are: 1)the thorax (no rotation) and 2)the foot in the stirrup. Everything else must move. When your seat reaches back your knees also must reach back. Move your arms back and forth with the movement of the horse; the elbows and hands give and take upwards rather than down. Give forward in every stride of canter toward the ears; up and away and then back, in the rhythm:
Photos courtesy of Karen Brown.