This article is from the Recreational Figure Skating FAQ, by Karen Bryden with numerous contributions by others.
The idea is that you get stronger and better at jumping by _doing_ it.
Repeatedly. In a row. In particular, plyometrics is supposed to
improve the explosive spring that is characteristic of all good
So, e.g., you stand there, feet shoulder width apart, take a deep
bend, and jump as high vertically as you can, keeping back straight
and bringing knees up as high as you can. Do this 20 times in a row,
rest one minute and do it again. The next time, bring your legs up
front together (a 'pike' position) and touch your feet with your
hands. 20 times and repeat. Then as in a Russian split. 20 times and
repeat. To a certain extent, you do this in ballet or martial arts,
but not to the same degree of repetition.
You can see that you'd be building some big jumping muscles, and
coordination. But your knees and back take an incredible pounding, and
that's why many ex. physiologists and trainers don't like plyometrics.
If you do enough reps to get the benefits, you may be very sorry. Much
of that depends, obviously, on your body, the surface you jump on, and
exactly how much you do.