I would quote almost everyone, but that would take too long.
In Battlefield 3, I tend to automatically hit the reload button every moment or so, even if my magazine is full. I also tend to switch my laser sight/tactical light off whenever I don't think I need it. In any game that has a save button, I repeatedly click it every now and then so that I don't lose any progress. For everything else, as I said above, almost everyone posted something that I have a habit of doing.