Like everybody says, its the quality of the jumps that counts, not getting tired and bouncing around like the 3 Stooges. Slow down, focus on each jump, 1 at a time. The first one may be kinda slow and ugly. You may feel uncoordinated. The next couple should get better and better. Then, one rep you'll jump and feel just like a rattle snake striking! Really fast and powerful. Like you didn't even jump, you just kinda twitched and exploded up onto the box. That's the rep you are looking for. The explosive feeling of the "excited nervous system." After that, do maybe 1 or 2 more jumps. The idea is to get a a few great jumps in before your performance drops off. Don't mess around with any slopping ones.
I agree with S. Butler. If 10 are easy, increase box height. You can also do "harder" jumps.
- Box Jump
- Higher Box Jump
- Sit on a Low Box, Jump from "box squat" position unto a High Box
- Step off a low box, recover, jump to a high box (depth jumps/plyometrics)
You can do throws or clap pushups or plyo-pushups for your upper body. Start with easy throws or pushups. Do a few single throws, till they are explosive and perfect. Move on to more complex throws.
Also, like Butler said do jumps/throws before you lift.
Jump rope and kettle-bell swings are cool ways to use "jumping" style moves for conditioning. I like to do these after lifting.