You need these 3 to reach your maximum vertical. Keep in mind that too much of each three can kill your vertical you need the right amount depending on your body index.
leg strength (squats and other leg weightlifting exercises)
Plyrometrics (stretching the leg muscles, teaching jumping muscle memory, and developing your fast twitch muscles)
Upper body weight ( Benching, and other weight lifting techniques)
Im gonna start with the most important one to me because i know most people dont even consider this when there thinking vertical, UPPER BODY WEIGHT. This is pretty much the secret for vertical training. If you have the right leg strength and have completed plyometrics training and you have no upperbody weight, then your body has no weight for your legs to propell it vertically, and you have actually voided your plyometrics and leg weight training at the same time. Think about this, if your throwing a baseball vertically in the air vs a wiffle ball (one that has no holes in it). Which one could you throw further vertically? The baseball because it has the right weight to power ratio for your arm. The wiffle ball is to light and cant propell be propelled upwards as far as a baseball will. In this case your legs would be the arm and your upperbody is the object being thrown.
Look at how big nate robinsons upper body is
Look at dwight howard, he has more upperbody mass than in his legs.
Look at a frog, the best leapers in the world. If they didnt have the body weight for there legs to propel itself upward do you think it could jump as high as it does? Because of the legnth of there legs they dont need to much body weight but it is still crucial.
But, putting to much excessive upperbody weight compared to your height will start killing your vertical. You want to find the right amount of weight to put on. Going back to the baseball example to prove why putting to much weight will kill your vertical. Throwing a baseball vs a baseball that weighs 5 pounds. Which one could you throw further into the air? Again you need to find the best upper bodyweight to leg strength ratio.
If you were to start your body from scratch, you should put on upper body weight first. Your legs will stregnthen normally because it will break down and build the right amount of muscle to carry your new upper body weight.
Once you finish putting on upperbody weight you should start your leg weight training. Again you want to gain the right stregnth and leg weight and not to much because extra muscle that is not needed will just weigh you down.
Once you finished your weight and mass training, its time to do plyometrics
This might be the hardest part of gaining vertical is plyrometrics. Plyro are exercises designed to teach your legs jumping muscle memory and developing twitch muscles. Doing plyro will teach and develop your legs to jump with your body.