Hold the airbrush like you would a pen, with your index finger poised above the release button and the air and hose directed away from the airbrush's tip. You can drape the hose over the forearm to keep it away from your painting surface.
Hold the airbrush perpendicular to the surface; this will allow the paint to spread more evenly. Don't hold the airbrush tightly; rather relax your hand, arm and upper body.
An important facet of using an Aztek airbrush effectively is understanding its components. Aztek classifies airbrushes through three main features: trigger action, paint-air mix level, and paint filling mechanism.
There are two main types of Aztek airbrush, based on the trigger action: single or double (or dual) action airbrushes---the former is the simplest form.
Single-action airbrushes spread paint lightly and delicately across the surface. You can control the flow of the paint with the trigger and through various tapered needles that come with the airbrush kit.
Something that distinguishes Aztek airbrushes from other airbrush types is that Azteks can mix several different colors simultaneously. Much of the artistry of airbrush technique thus depends on the finesse of control over the trigger---and this takes a lot of practice.
The double-action Aztek airbrush is more difficult to use, but gives greater control over paint flow---which is why more people use the double-action.
Press your finger on the button in the middle of the airbrush and begin the air flow. Let the air keep flowing, even when you're not making strokes with paint. Pulling back on the trigger produces paint.
Experiment with how hard you pull back on the paint trigger as well as the distance between the painting surface and the tip of the airbrush. Many factors go into what type of mark you produce, and the more you experiment the greater control you will have over the Aztek airbrush.