Use a ruler and a pencil to sketch a design on a sheet of scrap paper. You can bisect the space of the mural into a series of different shapes by using intersecting lines. Another option is to create a random arrangement of overlapping squares. Keep in mind that straight lines will be easier to tape off. Fill in colors with crayons or colored pencils.
Determine which color is the background color or is predominant in your mural design. This color will be the base coat.
Tape off around the outside border of your mural with low-tack tape. Run a putty knife over the tape to create a good seal.
Paint this base coat of the mural using a foam roller. If your mural stretches to the edge of the wall, you may want to fill in along the corners of the room with a foam brush. Let the base coat cure overnight.
Tape off the geometric shapes in the mural with low-tack tape. Refer to your sketch. You can use a yardstick and a chalk pencil to guide you, if you wish. If shapes overlap, plan to go through the process of taping and painting a few times.
Use a different foam roller for each paint color. Roll the paint on evenly to avoid needing a second coat of paint. Peel off the tape right after you paint each shape. Let the mural dry approximately 12 hours between painting and taping the next batch of shapes. If you don't allow enough time for the paint to cure, the tape may pull off the paint underneath.