I've got a couple,
In pokemon, when I take damage I hold the right button as though it will improve my defense, and when I deal damage I hold the left button, as though it will improve my attack.
In FPSes, I almost never use a shotgun, now I know alot of people probably prefer automatics, but I've only once used a shotgun in Left 4 Dead.
In RPGs that let you specialize in some skills, but still allow you to use other skills, I will choose the magic or similar specialization, then go ahead and use melee weapons for everything, like in Oblivion I chose ALL THE MAGIC SKILLS, but then I rarely used any of it, or in Mabinogi, I chose the Alchemist destiny despite knowing that most of my fighting will be done with a sword anyway.