When two or more people must share a lane, the custom is to swim in circles. That means you will always be swimming in the right side of the lane, and traffic coming the other way will be to your left. Stay on your side! Think of it as a two-lane road and the line on the bottom of the pool is a double yellow line -- no crossing over it. You need to stay to the right to avoid a collision.
If you do flip turns, stay to the right until you get to the end; then, do your flip turn on the left side of the wall so you won't spring off the wall into oncoming traffic.
Find the right lane
Practices should be organized so swimmers of comparable abilities and speeds swim in the same lanes. It's not a social or ego thing; it's common sense. You don't want to run over someone slower, you don't want some hot dog running over you, and you don't want to make everyone else mad because you're the one slowing down their workouts.
If you're not sure which lane you should swim in, ask. Don't pick the one with the fewest people -- there may be a good reason why there aren't a lot of people in the lane, like the difficulty of that lane's workout.
Let others pass
All swimmers are not created equal. So even if you're in the proper lane, you might not be able to keep up at all times. If somebody faster gets too close, simply stop at the end of the pool and let the person go by. Don't make him or her pass you in the middle of the pool. It's dangerous. Stepping aside is the right thing to do, and it won't slow either of you down.
If a slowpoke is slow to respond, gently -- gently -- tap his or her foot in the middle of the lane. The courteous swimmer will stop and let you by at the end. Only a jerk won't.
Share the water
It's not your pool. Remember? You just use a small space in a shared pool. That needn't be painful. Think of it as being guests at the same party. Be polite, or you won't be asked back.
Give courtesy a chance
What was once known as "common courtesy" is sorely uncommon today. Pleasantries like "please," "thank you," "I'm sorry," and "after you" have disappeared in our high-speed, high-tech society. So although you may not be able to change the world, you can make your little corner of the pool a more pleasant place. Your fellow swimmers will really appreciate it and might even be more courteous themselves. Courtesy is one of the nice contagious things.