The way I taught my kids was I put them on a lunge line with hands on their hips, chin up, eyes forward at a walk. Then I would tell them which leg was forward so could feel it, then I had them say left, right, left, right etc. I would stop have a little conversation then start back walking and have them feel for left, right etc. When they could feel the walk I started them trotting on the line and did the same thing, but said up, down, up, down and had them feel for the up and down. Then we did it with 1,2, rise, fall, I used different words just for variety. After a couple times on the line they could feel their horse and pick up the correct diagonal. I like having them on the line so they are not worried about steering their horse or keeping it moving all they have to do is feel and worry about what they are doing. So maybe someone can lunge the horse for you and so you can focus on the feel, without having to worry about the rest of the horse.