"Air Traffic Control" - Graham Duke
Quite a nice little introduction, though seems to contradict the material NATS provide for the ATC motivation paper on a couple of points which might be confusing if you read it before stage 1
If you can organise it then the best education you can get would be to visit a few ATC facilities.
What ever you do
don't watch Pushing Tin, its wholely unrealistic (though a good bit of fun).