An excellent choice that I am working on as well. The reason it is such a good choice and so difficult is the broad range of prerequisites required. Here is what I have found that you could look into.
1. Test how far you can raise your leg and hold from a standing position. Martial artists use this because flexibility and strength issues are sometimes confused in high kicks. You should have good motor control of the raised leg and enough strength to hold it. Often people can hold their bodyweight on a dip bar but can't hold up their legs straight. That beg's the question where the strength deficit is.
2. Hanging leg raise. Addresses core strength and hip flexor strength at the same time.
3. Do L-sit pullups. Just raise your leg as high as you can.
3. Dip bar holds. Simply raise yourself into the right position and engage the scapular and keep pushing so your shoulders do not shrug. Like the flexed arm hang, you might feel yourself start shaking. This seems to work the biceps really well as well. Any straight arm strength does.
4. Tricep isolation work. Make sure to fully lockout the triceps rather than keep the elbow bent.
5. Test your hamstring flexibility buy lying down and then seeing how high you can raise your leg. It is a basic part of the FMS screen. Yoga straps can help work this.
I suggest searching for "scapular strength" on youtube for workouts for gymnasts. This is a game changer. There are a lot of interesting exercises from gymnasts.
GTG.
1. Simply support your weight with
parallettes or pushup handles. This could be a work break depending on your work environment.
2. Raise your leg straight from a sitting position and hold with your toes pointed. If this is harder than you thought then hip flexor, leg strength and mobility issues need to be addressed.
The best thing about this exercise is that it helps so many things even if like me you have not achieved one rep yet.
There are lots of sources of information online about progressions, but I find that in most cases, taking apart the movement and figuring out where the deficit is and addressing that and then rebuilding with the full progression to be a more effective strategy.
Good luck. I hope we can both achieve it one day.