Prior to joining the RyuTe Renmei about a quarter-century ago, my instructor spent fifteen years doing Japanese Goju Ryu (lineage: Gogen Yamaguchi-->Peter Urban/Lou Angel-->Gary Boyd-->my instructor), and there are a few things that we've held onto from that system. One of them is an exercise developed by Mr. Boyd called "Kicking Exercise #1." I love this exercise. It is flexible. It is good for overall conditioning. It is good for balance, especially learning to keep your balance through multiple pivots and weight shifts. I'll describe it here as best I can (NO, I'm not going to show you!: Maybe someday when I've achieved such command of it that I can make it last a good four minutes or so.). Anyone who's at all familiar with any sort of karate, Okinawan, Japanese, or Korean, should be able to follow my terms quite easily.
Assume a natural stance, or ready position.
Move your right foot back into a forward stance (sounds contradictory, I know, if you're not familiar with it, but all it means is that your left foot is left in the leading position) and bring your arms down to your sides as though you were doing a low block on each side.
With your right leg, execute a side-thrust kick to your front, solar-plexus height. All of the kicks will be to solar-plexus height. Bring your hands up to a guard position as you do so.
When you bring that leg down, land in a natural stance facing the way opposite that which you started. That is, if your first natural stance faced north, you are now facing south.
With your left leg, execute a back-thrust kick in your original direction of travel. That is, if your side-kick went north, so does your back kick.
Land in a horse stance. Your chest is now facing eastward, so to speak.
With your right leg, execute a round kick to the "north," that is, toward the direction you were originally facing..
As you land, do so--this is difficult to describe--by placing your right foot down about two shoulder widths in front of your left foot and one shoulder width to the right of that foot. As your weight settles, pivot fully into a right-leg-forward forward stance. You don't want to CLOMP down into that stance, you want to PLACE your foot into position and then pivot fully into it.
Execute a front-thrust kick with your left leg. Land in a forward stance, left leg forward.
Look over your right shoulder, start to pivot your torso, and then move your right leg over and pivot into a right-leg-forward forward stance. Repeat the exercise on the opposite side.
You will have to adjust your position from time to time, as the exercise fairly obviously moves you over body-width by body-width as you repeat it.
What makes this exercise so difficult? Well, any idiot can do it fast. And if you repeat it many times at full speed, it can be a pretty decent little aerobic workout. But it really comes into its own when you do it with slow, continuous motion.
VERY slow, continuous motion. TORTUROUSLY slow, continuous motion. If you are not having difficulty maintaining your balance at some points throughout the exercise, you are not doing it slowly enough. The slower you can do this exercise, the better. And it works. As far as I can tell, doing the exercise this way improves all your kicks. Snap kicks in every direction, thrust kicks in every direction. If I had to limit myself to one, and only one way to practice kicking, I'm not at all sure that I wouldn't choose this exercise.
If you're interested in the Northeastern Oklahoma variety of Japanese Goju Ryu, here's where you need to start.