Like the guys said either feeding or on the way from food to bed (mornings) or from bed to food (evenings). I've never had much luck trying to sneak up on a sleeping Deer, they usually have a back way out and sleep with one eye open. But you can walk likely places, brush or a hedgerow, and spot the grass or weeds matted down. Just don't get too close and spook them off with your smell, I usually figure thirty yards is close enough. When I scout a bedding area I usually wait a few days before I show up in the area again. You don't want to spook them off their routine.
Always look behind what you are shooting at. I get tunnel vision and I imagine other people do also. I have to force myself to look behind what I'm shooting at, the bullet can go right on through a Deer. I got shocked out of my complacency early one evening when I scoped a nice Buck, he took another step and I was looking right at some guys TV screen through some brush and trees a couple of hundred yards down the hill. I'm really glad I didn't pull the trigger.