Tip $1 or $2 per person per night. Leave more if there were special circumstances--for example, if you made a mess of the room or required more towels or extra blankets. If you're staying in a high-end hotel, it is customary to tip $3 to $5 per person per night because such hotels are generally associated with a higher degree of service.
Leave a short note with the tip to indicate that it is for the housekeeper. Hotel staff are usually trained to leave any money they find in the rooms.
Place the tip on the pillow, where it will be readily noticed. A nightstand or desk top is also acceptable.
