Did the drill where the instructor tosses the ball to the side, we run to it, hit, sidestep back to the center. He said to make sure you move forward into the shot each time, focus on that. Really tiring, but good. Could feel the difference when I was leaning in as opposed to falling backwards or to the side.
He also gave us some pointers on volleying during the volley drill. Said to take short choppy steps while moving towards the ball, which helps maintain balance. Punch the ball, no swing. If ball is sailing, then pull back a bit after contact.