There are three players on the court, the rest are waiting for their turn behind the baseline. (see graphic below)
Player A is the server, B is at the net, and player C is the returner. The coach is at one of the net posts giving instructions to the players.
This drill is about teaching the player at the net how to position himself according to where his partner’s serve is being placed.
The player at the net needs to position himself properly after the serve is delivered so that he will be in the closest spot possible for an eventual volley.
Set-up:
There are 3 marks placed inside the service box:

1. Red: close to the singles sideline and service line.
2. Yellow: close to the service line and about halfway between the center line and singles sideline.
3. Blue: close to the center line and service line.
There are also 3 marks inside the service box where the server’s partner stands: red (wide), yellow (middle), and blue (inside – closer to the center line).
The net player begins the drill just behind the line of marks (precisely behind the yellow one).
Drill:
Player A hits 3 serves – anywhere inside the service box.
Player B will have to move and do a split step just above the spot that corresponds with the side (mark) that the serve was delivered to.
Example: If the serve lands close to the blue mark, the net player will step forward followed by a split step on the respective blue mark in front of him (see graphic below).
The same if the serve is delivered to any other mark inside the opposite service box, the net player will split-step where the respective colored marker is.
Player C, on the other side, will return every ball to the net player (B) for him to take a practice volley.
After every 3 serves, players rotate clockwise so that everyone gets to practice court movement and positioning at the net.
Note:
This drill, as you can tell, teaches the net player to move according to where his partner’s serve is being delivered. This action puts him in the best position to cover the court and be quicker for an eventual poach.

the right spot