There are a few things you need to know before setting your Roomba to clean one room. First, make sure the room is large enough for the robot to move around. Second, make sure there is no dust or dirt on the floor or walls. Third, set the Roomba to its cleaning schedule and make sure it is working on all surfaces of the room at once. Finally, be sure to keep an eye on it and if it doesn’t seem to be cleaning properly, take it down and start over.