Steps. 1  1. Select your spray paint. 2  2. Read the spray paint can to determine how much spray paint you will need to purchase. 3  3. Wash the plastic item you are going to paint by scrubbing it with soap and water to remove all dirt.  4. Sand the 1  item. 5. Place your plastic item in a well-ventilated area.  6. Shake the spray paint can well before beginning.