Though overhead presses, push-ups, etc. will help, I have a super-secret method to maximize your ability to handstand. It's pretty cool, because it utilizes some very scientific concepts to minimize wasted time. The trick is to make the most of neurosynaptic facilitation to prime the neuro-muscular system for maximum benefit. The methods for doing this are somewhat arduous, but it's worth it in the end.
Oh, and if you were wondering, neurosynaptic facilitation is just practice...and lots of it. Handstands on the wall, every day, shooting for 5 minutes inverted as a minimum daily, then trying to reduce the amount of help the wall is giving, then kicking up and fighting for the free-standing handstand, and doing this EVERY DAY, is the only surefire way to figure this skill out. It takes lots of practice.
Besides that, this might help a bit:
http://www.sandowplus.co.uk/Competition/Hoffman/YorkHandBalance/yorkhb1.htmthough I've found it most useful as far as tips and ideas for some of the more-advanced handbalancing skills.
