This may be getting repetitive, but before spraying any figure, thoroughly wash it with a detergent such as dish washing detergent and warm water. Rinse it thoroughly, and let it dry.
It is always best to prime your figures before spraying colour spray on them. When spraying your primer, start by spraying a light mist coat and let it dry thoroughly, and then spray a couple of light coats to finish covering the model with primer.
When you spray your colour coat, repeat the process. First spray a thin mist coat, then spray light coats until you have a good coverage, allowing each coat to dry before spraying the next.
You should spray the mist coat at about eighteen inches, moving the spray fairly rapidly across the figures. Spray your colour coats at approximately twelve inches with a slower and steady motion. Always start your spray before the figures and end it after you have passed the last figure. This process is very important, especially with the new Games Workshop Citadel Colour paints, as they are produced by Krylon, and they are a very strong enamel paint which will attack your plastic figures if you put too heavy a coat on. You must not let a truly wet coat touch the plastic, or the plastic will melt.
-Ragnar (Tom Setzer)