If you haven't read my first gymnastics post, please head back and check it out! It goes over the basics needed before training your horse to jump.
If you have read it, by this time your horse should be consistently and confidently working over trot poles and canter poles in various areas of your riding space. If you are unsure, spend a bit more time on those before moving on. You can also continue varying the trot and canter poles by raising alternating sides of the rails with a small riser. Jump Blocks work really well for these gymnastics -- Here is a link to a great set on amazon -
At this point we are ready to introduce the first jumps for your horse! My favorite way to introduce a jump is through the most basic gymnastic - 3 trot poles to a small cross rail. You already did the work of finding your horse's most comfortable trot step in part 1. Now, multiply that by two (yes, I know, math!!! We never thought we would use 'solving for x' after school!) and place a small cross rail at that point.
For most horses, This will be 4 feet between the trot poles, and 8 feet between the last trot pole and the cross rail.
How it feels: The horse may trot the entire exercise at first. While that's not the eventual goal, its a great starting point. The jump should be low enough that she can easily walk over it to see the distances. Ideally, the horse trots the 3 trot poles, and sets her feet together before the cross rail so that as she is in the air over the cross rail she is already in rhythm for a canter. The cross rail should feel like one elevated canter stride, because that's exactly what it is! :)
I suggest using this exercise many, many times. I still revert back to a version of this on my mare who is consistently jumping 2'3 - 2'6". Once the horse is confident and comfortable with a small cross rail, raise it up a bit to look bigger. This would also be a good stage to start incorporating some filler (decoration) to the jump. Start small, with a few fake flowers from the dollar store. Place them at the edge of the jump and progressively move them closer and closer to center, as long as your horse is accepting them and is not terrified of the horse-eating nature items.
This exercise can be adjusted to take up months of training. Lengthen the trot poles to get your horse to stretch a bit. See if you can really get your horse responsive to the jump! Remember, you are the confidence here. The rails themselves do the training to 'tell' your horse where to put her feet. Your job is to keep her straight and stay out of her way as she negotiates the challenge. There is no shame in grabbing mane, especially if it means avoiding yanking on her mouth in the air.
Once this is accomplished, Try varying your exit strategy. Can you get a left lead canter on purpose? Try alternating which direction you go after the jump and see how well your horse responds. Bonus points to the horses who can halt in a straight line afterwords! Halting straight is a great way to build up some extra balance, co-ordination and glutes!
Have fun, stay safe and jump on!