What are plyometrics and how do I use them?

Here are some good drills for runners.

Plyometrics are a good thing for building strength and running form. They come in the form of box drills and running drills.

Some drills that help runners are:
running in place, standing bring knee to chest, walking bring knee to chest with arm pump to balance, running in place or very slowly with high knees, running very slowly with a butt-kicking motion, hot-foot drills where you minimize your plant time, skipping for height, skipping for distance, and bounding.

I list these in order of stress - make sure you are warmed up and well stretched before doing any, and do not move past the first few exercises until they start

Here is an alternate list of low-medium-high intensity plyometric drills:
Low intensity - In place squat jump
Medium intensity - in place pike jump, double leg tuck jump, double leg hops, alternate leg bounding
High intensity - single leg hops, speed hops
Shock intensity - in depth jump, box jump

Remember that the point is to work your muscles, not to cover ground. Keep the feet moving quickly.