Whether painting on wood or poster board, sketch out the drawing beforehand. Sketch the drawing freehand -- know how you want your composition to appear. Select the colors for the drawing based upon preferences and portrayal. Start with a clean, dry surface.
Don't buy the cheap paint. Buy top-of-the-line paint to ensure the color quality that your spray-can art requires. Use the paint in a well-ventilated area and make sure the temperature is above 65 degrees when spraying. Otherwise, the paint might not spray properly.
John Matos, graffiti artist, created an art gift for friend Eric Clapton, in the form of a series of painted Fender Stratocasters dubbed "Crashocasters." The piece uses "aerobic, full-arm motion" when painting with the spray can. He moves slower for the thicker lines, and faster for thin ones.
Keep the paint can 12 to 18 inches from the painting surface to avoid runs. Use light applications, applying thin coats. Shake the can repeatedly before using to mix all the contents. If the can clogs, shake it and turn it upside down. Spray for five seconds to clear the spray nozzle.
Before beginning painting, always test the can on a scrap piece of material. Ideally, use the same material for testing as you will use for your canvas. Ensure the color quality is what you want and the paint sprays appropriately. Return defective cans for a refund.
Read the spray can directions before using. Pay attention to the tips offered on the can, and note the drying time between coats. If you don't allow enough time to dry before applying a second coat, the paint may run and ruin the art piece.