To airbrush, hold the brush in the same manner as you would a pencil or pen. Place your index finger on the trigger, keeping your grasp relaxed and loose. Hold the airbrush perpendicular to the canvas, and quickly, fully depress the trigger to spray paint onto the surface.
One of the most integral parts of airbrushing is learning to spray dots. Dots are the building blocks of airbrushing, and the accumulation of them fills in your outline. Keeping your hand still, spray close to the surface to create small dots with defined edges. Spray at a distance to create larger, less defined dots.
To create a line, depress the trigger and move your hand as you spray. Avoid creating a large dot at the beginning of the line by moving your hand before you start spraying. Stop spraying before you stop moving your hand to avoid making a dot at the end of the line.
Keep the air on your airbrush turned on while you are using it, even between paint strokes. Use the air compressor, not the trigger, to regulate the amount of air that comes out of your brush. Drape the air hose over your arm to keep it out of the way as you work.