few tips.
1. For original panels that has rough surfaces, such as the plastic panels from the Proton cars, it will be advisable to sand the surface with the lower grit sand paper to as flat and smooth as possible, then slowly increasing the grit number to a higher one to get a smooth flat surface. That way, the quality of the paint would be better.
2. Before spraying, take a pail, fill them with hot water, but not boiling hot water, just a little warmer water, put all your spray cans into the pail, this way would increase the air pressure from inside the spray cans and will result in a better efficient in the nozzle, and also the spray air coming out
3. When using spray can, always remember to place the item to be painted as high as possible near your hand level so that when you spray, it would be high as your waist line and you dont have to face the nozzle that low, spray with the nozzle facing around 30-40 degrees down, that way you get the best effect.
4. lastly, patient must be there, spray as thin as possible, one coating by one coating, and leaving them to dry around 5-8 minutes per coatings before continuing. The more thin coatings you can apply, the better and thicker and nice the end results will be. We cannot use the technique used in normal car sparying because they used pressurised air and the paint material is different and they even mixed them with thinner, and better nozzle tips, thats why they can spray more and less coating but still getting good results.
hope this helps.