As well as timed intervals, I like to do counts. So many jumps without a miss before I do a strength exercise. Or do a “punishment” exercise for a miss. Try to best your count each time.
You can also do this same thing, but use both count and a time. It forces you to jump faster in the same amount of time.
You can also jump on one leg, then the other and add in directional changes on those individual legs to increase the challenge.