Play is the exultation of the possible. -Martin Buber
Start with APK Warm-Up 2
Handstand Pushup Training
Handstand pushups (HSPUs) are one of the hardest bodyweight exercises to master, with infinite variations possible.
Start with decline push-ups with your feet raised as much as possible to achieve full range of motion.
Then work your HSPUs against a wall, either just the negative (lowering) portion or the whole movement.
If you can do several reps at this intensity, start adding a little range of motion by raising your hands on blocks (textbooks work well, or parellettes).
Work towards a free-standing HSPU, then an increased ROM free-standing HSPU, then an HSPU on rings, then a free-standing HSPU on rings, then add a weight vest, then do them one-handed, then one handed on a ring with a weight vest!!
Most importantly, spend 30 minutes challenging yourself with this skill.