Negatives are one of the most effective ways of increasing you hand balancing skills. Obviously, they can only be used for movements and not holds. If you are working on any kind of press negatives will help you get there.
A negative is the part of the movement where you descend. Lets say you are working on doing a straddle press. First you would get up into a handstand. The negative would involve you lowering your legs down to the ground, just like the press in reverse.
When you first begin these your legs may drop like rocks. As you continue to work on the movement you would strive for complete control.
If you can get to the point where you can pause and hold yourself during the descent then you are in good shape. Even if you can do the press normally, this is a great way to build more strength especially in the sticking points.
Just the other day I did a negative Tiger Bend for the first time. The negative involves going from a handstand into a forearm stand. This being my first successful attempt it was not pretty. I just fell to my elbows but I was able to hold the balance. In time, with more control, it will pave the way to doing real Tiger Bends in the future.
This method of training is much better than just trying to do the movements alone. If you have not been using negatives now is the time to start.