A great "on your toes" volley drill is with a partner, to start lined up on opposite diagonals as in the diagram below.

Then one of you feed and start to move in OPPOSITE direction to each other - you should try to meet in the centre at the same time.

The idea is to keep the volley going between you and your partner whilst moving across the court.

This is a great drill for working the volley and changing the direction of your volley.

TIPS
Have a couple of spare balls each as you do this drill, so if there is an error,one of you can feed another ball and so keep the drill going.

Also although the idea is to volley over the distance,if the ball bounces,then practice a half-volley or short drive again to keep the drill going.

Maybe do the drill for a set time and see how many times you cross the court without making a mistake.

Have fun!