Painter's tape is useful for far more than just covering up trim and ceiling edges when painting walls. It can also be used to plot out stripes of consistent or varying widths, such racing stripes along one side of a wall in a boy's room; interlocking squares, or virtually any other design you can think of that requires straight lines. Use a quality painter's tape to ensure clean paint lines; some bargain tapes may not stick well, resulting in paint that seeps under the tape.
Prepare the walls for priming by cleaning them thoroughly and allowing them to dry completely. Cover areas that you don't want to paint, such as baseboards and the edge of the ceiling around all project walls, with painter's tape. Place a drop cloth or tarp on the floor in front of the walls to protect the floor from drips and spatters, then paint the walls with one or two coats of the base or first color of latex paint, allowing it to dry for 24 hours. Use a roller to provide the most efficient paint coverage for the base coat.
Plot out a design, such as a large vertical racing stripe, by determining how far you'd like it to start from the edge of the wall -- 10 inches, for instance. Draw a mark at 10 inches inside the edge of the wall using a tape measure and pencil, using a laser level to guide the placement of tape all the way up the wall. Move closer to the middle of the wall approximately an inch and apply a second strip of tape, parallel to the first, repeating the process once more with a third piece of tape. The racing stripes are the area between the tape pieces; cover this area with the second paint color.
Create interlocking squares using a laser level to plot out horizontal and vertical lines along the walls, using chalk as a guideline. Use a piece of posterboard or construction paper as a template for the shapes, tracing around them in chalk as you hold them straight along the wall, or diagonally. Apply a tape border along your lines to create a square or rectangular "ring," repeating the process with an overlapped "ring" to create interlocking shapes. The same process can be used to create interlocking circles or diamonds.
Place tape on a diagonal for diagonal stripes, with all the tape lines evenly spaced from one another. Cover the entire wall or just a corner or two for visual interest.
Create a series of connected "V" shapes with tape on the wall, row after row, each evenly spaced, for a chevron pattern.
Turn a wall into an abstract art statement by arranging straight lines of tape at various angles across the wall and at various lengths, similar to a shattered glass pattern. Paint over the entire wall, then remove the tape to reveal the design beneath.