know where to stand.... and when to move.
The pickleball court is about 1/4 the size of a tennis court. This is a bird's eye view of the layout:
When your side has the serve, both players usually begin by standing behind the baseline. The first server is the person on the right side, and he must not step on or over the baseline during the serve.
When your side is receiving the serve, the receiver is the person diagonally opposite the server. The receiver may stand wherever he/she wants, but usually will stand behind the baseline. The other team member stands close to the "No Volley Zone" line, on a diagonal, so she or he can watch the serve and determine whether the serve stays inbounds. Only the serve goes to a specific player. After the serve, the ball may be hit by either player.
Both the serve and the first return must bounce one time on the other side of the net before being hit. Therefore it is important for those players to stay near the baseline until the second volley is hit. Then it is usually advantageous for players to move up to the no volley line. However, one of the early learning challenges is that a player is not allowed to stand in the 'no volley zone' or, 'the kitchen' as it is called in my group, unless the ball bounces within that area before a player steps in and hits it. Notice how the players in the picture below are at the no volley line, with the exception of Mr. Red.
Another facet of knowing where to move is to remember that the server on the serving team moves from the right side of the court to the left side, and back, until the service is lost. So, the server's partner must move from one side of the court to the other. However, the receiving players do not switch sides.
Here's another action shot. In the picture above I believe that the server was on the far side of the court in the light shorts. He served the ball to the fellow in the black shirt. The black shirted guy returned the serve and is moving forward to be in an optimal position to hit the ball being returned by the guy in black shorts. The players on the far side will most likely move closer to the net when the shot is completed.
Have I confused you? Lost after the first paragraph? I was lost for the first week of playing. My ever-patient partners were great at reminding me where to move. Sometimes I still need reminders!