Splitting the Lane 101
If you're swimming freestyle in your own lane, the line at the bottom of the pool is the ultimate guide to navigating in a straight line. But if you're splitting the lane with another swimmer, that line isn't quite as helpful.
One of the other ways to keep track of your placement in the lane—and to avoid any painful head-on collisions with your lane mate—is to keep your eyes on the lane line while you're breathing. If you're a bilateral breather, this means using every other breath (or every six strokes) to also check to make sure you're snug against the edge of the lane where you should be.
If you prefer to breathe every other stroke, make sure you're breathing on the side closest to the edge of the lane so you can constantly monitor to make sure you're not straying into oncoming traffic.
Circle Swimming 101
While it's ideal to find swimmers who are about the same speed as you if you're circling the lane, this isn't always possible. This could lead to some issues that you need to know the solution to.
Giving space: If a swimmer is faster than you, make sure you don't start another lap just as he is coming up behind you. If you start about 5 seconds behind a faster swimmer, you will probably never run into each other during your workout.
If you're at a comparable pace with your lane mates, make sure there is plenty of space between everyone. If you do this correctly, you will barely even notice anyone in your lane.
Passing: If a faster swimmer is coming up on you and touches your feet, that's an indication that they want to pass. Swim to the next wall, then stop and let them go ahead of you.