Say you have an empty wall and an empty wallet. Luckily, there is a very simple solution to your problem: free paint chips!
These little cards can be found in the paint section of any decent hardware store. Just walk in and grab a variety of colors. The only other things you need are a pair of scissors, painters tape, and some creativity.
I got the idea stopping by a house where people had taped a bunch of chips to the wall in a much more abstract pattern, so credit goes to them, whoever they are. Also, after writing this up, I realized there is a similar instructable here, but I figure that this is different enough to get its own.
This is a great way to make a space your own, especially if you are in an apartment or dormitory where they get grumpy about thumbtacks and screws. I know when I lived in a dorm, blue painters tape was the only thing allowed. Also, the irony of decorating with paint samples is enjoyable in its own right.
Step 1: Prepare the Chips
Usually the chips come with three similar colors on each one, separated by little white strips.
I decided to separate the colors, and trim off the white strips.
You might decide to leave them on the same card, since they do look kind of cool that way. Or maybe you want to cut them into different shapes. Triangles, circles, amoebas, whatever!
Step 2: Layout on Floor
To make sure your design fits on the wall, measure the space you are trying to fill with a tape measure. Then, tape out that rectangle on the floor. This is your canvas.
Spread your chips out on the ground, and figure out a pattern you like. Its much easier to do it this way, since you don't have to mess around with tape while you are moving things around.
Once you get a design you like, take a picture. That way you can keep moving things around to experiment with different ideas, but can still go back and recreate older ones.
Step 3: Transfer to Wall
Alright, now that you have a design you like, time to transfer it to the wall. Using your picture as reference, move a few chips at a time. A little roll of painters tape on the back of each one holds it to the wall, but lets you reposition it a few times before it loses the sticky.
Step back and enjoy!