Spray painting is great for giving a figure a even base coat or for covering large areas. There are a few things you want to be careful about when using spray paint on action figures and vehicles.
Spray paints made for use with plastics
The paint needs to be made for plastics. Some of the spray paint solvents can actually melt plastic. Because of that most customizers use Krylon Fusion, Krylon Camo System, Rustoleum Universal, automotive paint, Tamiya spray paint, or Testors Model Masters spray paints. Recently automotive vinyl interior paints made for restoring plastic dashboards and consoles have been used with great success.
Be sure to spray in a well ventilated area. Spray paint fumes are highly flammable, and can cause respiration problems. Not to mention they can make your boogers olive drab or Cobra blue.It is always best to wear eye goggles and a breathing mask.
Check weather conditions
Moisture and temperature will effect dry times and smoothness of the coat. The spray cans are temperature sensitive. Too hot and they spray like a soda can left in the hot sun. Too cold and the propellant and the paint won't mix very well. Try to keep the cans at room temperature even between spraying coats. Cracking will occur if their is a problem with the curing of the paint.
Don't over spray
You won't ever get everything on the first pass. It is always best to do multiple light passes with plenty of time in between instead of trying to get everything in one or two heavy coats. The thicker the coat of paint the more detail you will lose in the end. Go over the item very quickly, very lightly the first time. Then wait for it to completely dry. The dry time depends on the brand and surrounding conditions. Something like Krylon Camo on hot sunny day can dry completely in 15 minutes. On the other hand Tamiya silver can take an entire day to dry if it is raining that day. Once it is dry, flip it/turn it, and spray another series of light passes. Wait for it to dry again. And then touch up any spots with a third series of light passes if necessary.
Spray and walk away. Give it several hours to dry. Most of the problems people have when using spray paint have come when they try to rush things and either over spray or don't give enough time to completely dry.
Ways to fix too glossy or too flat spray paints
Also a dull clear coat will cut down on the glossiness of the spray paint and a semi-gloss clear coat with make a flat spray paint shinier.
Some rubbery types of plastic won't take any kind of paint and will remain tacky no matter how long you wait. Cracking in the paint can occur if their hasn't been sufficient dry time between layers, contaminants like dust or pollen have gotten onto the item, or if the plastic has some type of remaining oil on its surface. Sand away the offending areas, wipe down the area with soap and water, respray with light passes, and then bring inside to dry if you can.
Be sure to check out the Basic Training video tutorial.