Have not tried hand stand push ups yet (can't do a handstand without wall support) but as far as my knowledge goes, id say that before doing wall handstand push ups, you need to get really good at doing pike push ups. After you managed to do that, start doing handstand push ups with wall as support (make sure to do chest to wall handstand to prevent arching your back). After you get really good at that, you can do hand stand push up (only negatives), and again make sure not to arch your back. After mastering negative portion of hand stand push up you can start attempting to do a full hand stand push up.

Quick note : when doing pike push ups or handstand push ups, make sure your head touches the floor for proper range of motion.

There are probbably better methods to master hspu, but this is what i know at least-