To improve your vertical jump there are plenty of great exercises you can do. Squats and deadlifts for strength, skipping and bounding for reactivity, and box jumps for rate of force development to name just a few. However, above all of these in terms of effectiveness stands one exercise that should be in ALL jump programs.
This exercise is far more specific to your sport than any of those others. It will develop all the athletic attributes needed to jump high including the often overlooked area of movement efficiency. Even better, this particular exercise is insanely sports specific. No other exercise comes close.
So what is this magnificent jumping exercise that trumps all others? The exercise I am referring to is none other than going out and performing some maximum effort jumping. Yep, it is that simple. The shortest way to get somewhere is usually the to take the direct path. Vertical jump improvement is no different.
If you are trying to improve your jumping ability for a sporting pursuit, then the simplest, and most effective way to go about it is to actually practice that skill. Volleyball spiking is a great example. You need to time the jump as well as co-ordinate yourself to hit the ball with a lot of force, all while in the air. This isn't as simple as just jumping up straight and down in the air. In the early stages the movement will often feel unnatural, but the more you do it the more fluid it becomes and the higher you will jump.
Sadly, despite the obvious benefits that doing sports specific jumping practice has, it is rarely included in any of the vertical jump programs you can buy. Vertical Mastery is about the only one that does. People often believe they need all sorts of fancy exercises, different sorts of weight training equipment, and cleverly designed programs, but it is amazing how often they overlook the basic act of going out and simply doing some jumping.
Practicing your jumping technique will help you jump higher in a variety of ways. The first thing it does is makes your jumping motion more efficient. This improvement offers up some potentially huge benefits. If you have less than stellar co-ordination then you will be severely limiting your potential jump height. It results in you not being able to coordinate your muscles and joints to fire in the right order and with the right power to maximize your jump height.
Practicing jumping also helps develop explosive strength and reactive strength in a manner specific to jumping. The other exercises such as skipping, bounding, weighted step ups, squats and so on all help develop those things as well, just not as well for jumping as actually jumping.
In essence any athletic training you undertake is designed to force your body to adapt. So in order to get stronger you need to consistently get into the gym and lift progressively heavier weights. In this way you send signals to your body that you require it grow in order to meet those continuously higher demands. The same goes for jump training. If a massive vertical jump is your goal, then you have to go and keep trying to jump higher. The more you practice jumping high the greater reinforcement of the message to your body and the quicker it will adapt.
One thing maximum effort jumping doesn't do well is to develop a good job of is increasing your maximum strength levels. Weight training is a clearly superior approach for this. Getting stronger can be very important (and beneficial) if this is your weakness. But unless you have sufficiently developed your movement efficiency first, any strength gains will not necessarily carry over to an increase in jump height that well.