Make sure you have proper ventilation in your work area and / or a chemical cartridge face mask. Your health and safety should always be your first concern.
Room temperature (65-75 degrees) is optimal for spraying primer. Cooler is better than warmer. Applications below 60 and above 80 degrees are not recommended.
Make sure your primer is sufficiently thinned to suit your environment and method of application. By environment I am primarily referring to the room temperature. Warmer temperatures may require more thinner to be added to your primer mixture to help increase flow. Better flow means less sanding.
Have the mold lines been removed? Sink marks filled? Do any panel lines need to be scribed? Is the surface scuffed for primer adhesion? Has the material been washed with a detergent soap and thoroughly dry? Is the surface free of dust and other contaminants? If so, then you're ready to prime the surface.


Agitate the primer prior to any application. Chemical components settle quickly. If you're using an airbrush jar periodically agitate it while airbrushing. If you're using a color cup agitate the primer prior to refilling the color cup while airbrushing.
Apply one or two moderate coats, let dry, then check the surface for flaws. Repair if necessary and repeat.
Once you're satisfied with the quality of the surface area then apply a heavy coat, let dry, then very lightly sand with 3600 grit cloth. Heavy coats have better flow qualities and fewer overspray problems but would have a tendency to run without the lighter coats applied earlier to give them something to help adhere to.
Apply a heavy coat, let dry, then very lightly sand with 4000 grit cloth.

Remember that the primer is there to protect the surface area from the lacquer's hot solvent base. For this reason no surface area should be exposed at this time. If so, repeat primer applications until the surface is sufficiently covered. Allow your completed primer application to dry overnight before applying any color coats.

Remember while priming to also spray the underside of edges (body panels, wheel wells, etc.) to help prevent chipping or flaking of primer and / or paint during later stages of polishing and assembly.

Cleaning your airbrush equipment can be done by using either primer thinner or acrylic lacquer thinner.