Don’t assume, because you are going to a pool full of water, that you won’t be thirsty when you get out. Chlorine is not thirst-quenching.
Don’t wear your most precious jewellery to the leisure centre as the heart attack that ensues when you can’t find it, even though you know you stuffed it right into the toe of your trainers, is not fun.
If you find that the person before you left their pound in the locker, smile and pick it up, but beware that nothing comes for free. In this instance, I spent the entire session panicking that I wouldn’t be able to get my clothes back, as the key wouldn’t turn when I tested it before swimming. (I eventually managed to prise it open).
Don’t rush to change back into your outside clothes. Trying to pull on jeans when you have wet legs is not easy and to hurry this task will only result in further frustration and eventually tears.