Sometimes, even if the room looks good it can get boring. If this is the case try rearranging furniture, pictures, and nick-nacks.
I like to keep neutral base colors in the house so that I can change the accent colors when I feel like it. This will give the room a new feeling for very little cost, time and effort. I am always on a very tight budget but there is still a lot you can do with very little. Paint and spray paint are two of my best friends. I paint everything when it starts looking old and tired or even if I just need a change. Another thing I hope to do eventually that doesn't cost a lot, is buy a couple of sets of curtains. You can get curtains for pretty cheap at places like Wal-Mart, Target and Ikea, or you can make you own. You can then change your curtains with the seasons or whenever you get the urge.
And of course there is painting the walls! I love painted walls. This is such a cheap and relatively easy way to change the whole look and feel of a room.
I really find that when things look good I am more inspired to keep them clean.