Keeping each player on their preferred side, whatever the score. An advanced skill: you probably won't use it at crew or rec play, but you'll see it.
In doubles, where you stand depends on your score. At an even score you're both on your starting sides. At an odd score you've swapped. Stacking is how a team gets around that: you line up so each player can get back to their preferred side right after the serve or the return. Talk it through with your partner before the game. It only works if you both know the plan.
Our score is even: business as usual. R on the right, L on the left. Whoever the serve comes to stays back to return it; the partner is up at the kitchen line.
Our score is odd, serve comes to our right: L starts at the right baseline and R starts at the left kitchen line. L returns and immediately heads to the left side. As soon as the return is clear, R slides right toward the middle and protects L's approach to the line.
Odd score, serve to the right. L returns and crosses left; R slides right to cover the approach.
Our score is odd, serve comes to our left: R starts at the left baseline and L starts at the right kitchen line. R returns and immediately heads to the right side. As soon as the return is clear, L slides toward the middle and protects R's approach to the line.
Odd score, serve to the left. R returns and crosses right; L slides left to cover the approach.
Our score is even: business as usual. Each of you serves from your normal spot.
Our score is odd, serving from the right (R's home side, L's serve): you both start on the right side, with L serving. After the serve, L moves left along the baseline and R moves into position on the right. You're both back and ready for the return.
Odd score, serving from the right. L serves, then slides left; R takes the right.
Our score is odd, serving from the left (L's home side, R's serve): you both start on the left side, with R serving. After the serve, R moves right along the baseline and L moves into position on the left.
Odd score, serving from the left. R serves, then slides right; L takes the left.
Once the stack has sorted itself out, you're hitting the third shot. As a rule of thumb, you've got three good options:
Getting forward after the third shot is its own skill; Positioning Basics covers why the serving team starts on defense and how to move up together.