This can be a tough one. When you're exhausted and still have to fix dinner and put away the laundry, it's easy to postpone other chores. Your son is probably watching, though, and the extra minutes you take to put those slippers back in the closet or stuff that dirty towel in the hamper will teach him by example.
Now, the next time you mention that his books belong in the shelves and not on the floor, he'll remember your actions and be more likely to oblige without a fuss. And as much as you don't want to do it right now, that will be one less chore piling up for you to do later on.