I don't know much about geocaching....
But, I do know a bit about GPS.
And I know even more about paper maps, and how they have yet to be replaced.
So....
Bone up on your map and compass, paying particular attention to UTM. This will allow you to understand the foundational concepts of maps and coordinate systems, and how we find direction, then to that, you can add GPS skills that will give you that extra edge.
But note - GPS does not replace proper maps, and if you fail to understand real map and compass work, you are setting yourself up for failure.
Try....
Back Country Navigation for the Hunter, Compass & Position Plotting
by Dick Blust, Jr.,
http://www.kifaru.net/plot_blust.htm
http://www.kifaru.net/navigate1.htm
http://www.kifaru.net/compass1.htm
http://www.kifaru.net/GPSing.htm
And then later, you might buy the John Carnes book.... "Using Your GPS with the
Universal Transverse Mercator Map Coordinate System" which is a great value, and it comes with one of his map tool/roamers. Which are quite nicely made.
If you would like to get a taste of his writing, try....
http://maptools.com/UsingUTM/
And then, as your Jedi like navigation skills grow....
Land Navigation Handbook by WS Kals
Marion