Overall, the video guide is pretty good, but I would make a few suggestions to conserve energy and thus improve your score.
1) The author of the video suggests keeping your arms at your side. I found keeping my arms straight down and keeping both my forearms at around 60-90 degreesmade it easier to minimize the amount I had to move my arms to hit the hand balls. This also helps with balance, if that's an issue you're having.
2) Throughout the majority of the video, the actor lifts his leg to hit every foot ball. This almost always is not necessary. Simply having your foot on the ground (see around 1:40 of the video) works. It would seem anywhere from the knee down counts as "feet".
3) Keep yourself centered. There will be clusters of balls hit to one side or the other but be ready to JUMP back to the middle.
4) Lean your torso for most of the head balls to keep yourself centered. Rarely will you have to move out of center position for a head ball (unless you've already had to move for a hand/feet ball).
5) It pays to remember that each volley eventually lets up and reverts back to one server. There is a brief pause as the extra servers run off the sand. The first time this happens is on the 18th serve. The time when there is just one server is the best time to catch your breath and have minimal movement from your center position.