Standard variables...

I tend to have a status variable which can be one of a few states (e.g. sleeping/awake/dying/dead). Like objects are sleeping until the player nears them (e.g. in a platform game when the object is just off screen). Once close enough they are awake and behave as normal. If the player moves too far away they revert to sleeping. I found this helpful for keeping enemies in the right place at the right time (as well as saving on processing time)

Also animation direction/frame/timer/interval variables