A's, B's and C'c

High knees or  “A’s”
Just like it sounds. Drive your knees skyward with each stride, like a drill major in a marching band. Don't worry about forward speed. Simply lift those knees high. This drill strengthens your hip flexor muscles and improves your push-off power.

Butt kicks or “C’s”
Almost the opposite of high knees in that you're doing an exaggerated back kick. Literally, you should be "kicking your butt" with the heel with each stride. This drill stretches and strengthens your quadriceps muscles.

Skipping
Yep, just like you used to do in grade school. Use a slightly exaggerated arm motion to propel yourself upward and forward. Skipping improves your coordination and push-off power.

Bounding
As if you were jumping from one rock to another, exaggerate your normal running stride's height and length. Run in slow motion, alternately letting each foot do all the work of absorbing impact, then pushing off. This drill improves coordination and strengthens glutes and calves.