Most recreational badminton in the US is doubles, and the single biggest thing that separates a smooth doubles pair from a confused one is rotation: knowing where to stand at each moment of the rally. The rules of thumb are simple once you see the idea behind them.
Two formations
Attack (front and back): one player near the net, one at the back. You use this when your side is hitting down. The back player smashes and drops; the front player stays a step or two behind the front service line, racket up, ready to kill any weak reply at the net.
Defense (side by side): each player covers one half of the court, standing about mid-court. You use this when your side has to hit up, because the opponents are about to attack and you need to cover a smash to either side.
The one rule that drives everything
If your team hits the shuttle up (a lift or a clear), move to side by side. If your team hits the shuttle down (a smash, a drop or a push that makes the opponents lift), move to front and back.
Almost every rotation follows from that. You are always reading who is hitting up and who is hitting down.
Common rotations
From defense to attack: when the opponents lift to your side, whoever is in the better position goes back to hit. The partner moves forward to take the net. You are now front and back.
From attack to defense: when you or your partner lifts, the front player drops back to the side they are on, and the back player moves to the other side. You are now side by side.
Back player crosses: if the back player is pulled to the far corner, the front player shifts toward the middle so that the open side is covered.
Serve and return
After a short serve, the server usually stays at the front and the partner covers the back, so the serving team starts in attack shape. When returning a short serve, attack it if you can: push or net it down and follow in, then let your partner cover the back.
Habits that help right away
Talk: a quick "yours" or "mine" saves a lot of points, especially on shots down the middle. Agree on the middle: a common default is that the player on the forehand side takes shots down the middle. Don't both chase the shuttle; trust your partner's half. Recover after every shot back toward your formation position instead of watching your shot.
Practice tip
Ask your partners to play a few games where you only say the formation out loud: "attack" when you hit down, "defend" when you hit up. It feels silly for ten minutes and then it becomes automatic.
