Measure the thickness of your wetsuit. Wetsuits designed for tropical climates are generally too thin to paint; however, cold-water wetsuits with a thickness of 5 to 7mm are able to absorb neoprene cement safely, according to The Aquaflite Color Selector website's information on neoprene colors.
Purchase your selected neoprene cement, which typically comes in black and yellow colors although violet, blue and lime colors are also available at most surfing or diving-supply stores.
Practice painting the wetsuit with a dry brush (no adhesive) and practice using the neoprene on scraps of material before using the neoprene on the actual wetsuit. This lowers the risk of mess-ups which are then hard to reverse as neoprene dries so rapidly, according to Air Speed Press' information on wetsuit and drysuit maintenance.
Use small amounts of neoprene at a time when painting the wetsuit, as building on existing paint is a lot easier than trying to use too much at once. Paint until desired look is complete. Change colors by rinsing your brush with water before applying a new shade.