Follow the swimming direction
As you have probably noticed, the swimming direction in the pool is the same as on European roads, on the right-hand side (anti-clockwise). If this is not followed, a collision is generally unavoidable. And if you're behind it, you will most likely be in for a telling off at best and a slap on the wrist at worst... A very unfortunate situation as I am sure you will agree!
However, even if the vast majority of people know this, some swimmers, whether they are aware of it or not, tend to veer into the middle of the lane to be comfortable. This is very restrictive for other swimmers who must, for some, reduce the amount of space they are taking up in order to let them go past, and for others, be forced not to overtake for fear of colliding with another swimmer.
It is also very important to note that when you get to the wall, you must make your turn on the left-hand side of the lane. If this side is occupied by swimmers having a rest, the turn can be made in the centre but never, ever to the right!