This sounds silly to even write about but when people come into my lab, they always comment on what a good idea this is.
Kindergartners (heck, many 1st, 2nd, and 3rd graders) do not know their right from their left. Therefore, when I tell them to just press the left side of the mouse, that is not helpful at all. I solved this problem by putting a sticker on the left side of the mouse. Now, I can remind them by pressing on the sticker side. On the rare occasion that we do use the right side of the mouse, it’s easy enough to refer to the “side without the sticker!”