Monsters are doing something when you come across them. This is a nice little random table to help you figure out what they are doing, which also gives a nice narrative context for the encounter. Roll the "in lair" percentage to determine if you found them there or "out and about".
1 -- Sleeping (in lair or some temporary location)
2 -- Eating (preparing, devouring, chewing on bones, etc)
3 -- Resting (includes relaxing and playing)
4 -- Fighting (same species for territory or mating rights, or another species for territory or food)
5 -- Traveling (going somewhere, 50/50 to or from lair, or hunting something)
6 -- Stalking (the PCs, that is. Yeah, it's on.)