Be sure to run a few practice strokes after changing paint color or mix. Also, all paint brands and types are a different consistency.
In the beginning you can practice with dyed water to learn how to "feel" your airbrush action. Then you can move into very inexpensive paints to practice strokes and other techniques. Just remember that all paint is different, sometimes even cup to cup. You can sometimes use thinners to get materials to "feel" better. You can change your pressures, your needles, your airbrush, and so on... it really is an art.