Pick up an issue of Xtreme RC or RC Car Action whenever you can. They usually have at least one article which teaches you how to tune or improve your car in one way or another. Better yet, if you find that you like one over the other - subscribe to it!The best part about the tuning articles in these mags is that the same theory applies across all kinds of vehicles... just how much a change affects your handling varies from one specific model to another.
For example, this month's issue of XRC featres an article where Travis Amezcua (AE Driver) runs through the new B4 buggy and explains how each tuning change affects the handling of the car.
Another aspect of the magazines is that over time, you will learn to understand the meaning to many of the terms you hear, but don't understand yet.
Finally, don't be afraid to ask other racers, particularly those who have the same car as you. 9 out of 10 guys will usually be willing to help. Just try not to ask them 500 questions all in one sitting. After all, the whole point of the hobby should be to encourage more people to become a part of it!
To answer your question directly, that's how I learned everything I know.. .I read a lot, I asked more experienced racers when I was confused, and I did some experimenting for myself as I learned more.
Oh, one last thing... if you have specific questions, don't be afraid to ask your questions in the Rookie Zone Forum... I'm sure that plenty of experienced racers, like myself, stop by once in a while to see if they can be of any help.