Reddit mentions of The Ultimate Airbrush Handbook (Crafts Highlights)

Everyone learns differently. Some like videos some like easy to follow books.

There is no substitute for practice.

For video, start here but you can find others on YouTube. Towards the bottom look at "Airbrush Control Exercises"
http://www.airbrushtutor.com/tutorials/

He also has this very good tutorial "How to Control an Airbrush"
http://www.airbrushtutor.com/how-to-control-an-airbrush/

For books, I like these:
A Beginner's Guide to Airbrushing

and All About Techniques in Airbrush. I keep this book on the shelf near where I paint because it has an extensive troubleshooting guide that has helped me more than once.

I would get some cheap liquid watercolors or cheap acrylic paint that you can water down for practice. Get some water color paper to practice on. You want to practice making all size of dots and lines until you can get exactly what you want. It takes some practice. Then you want to practice making shaded cubes, triangles and circles. The books have examples but they are online as well. When you feel ready, get some cheap snap together plastic models of cars, tanks or jets and practice blending and getting gradient colors and details.

Hope that helps. Patience and practice will get your skill level up.