Vince, running 'low level' races will never make you a good navigator since the pace is so quick that, as Chris has said, if you stop to take your bearings, your race is over.
Iains suggestion is sound but so also is reading up on it and then going out into the hills on your own and realising just how straightforward 'simple' nav really is. Its really satisfying to be able to plot a route, dial it into the compass and then run, head down and see how accurate and easy the technique is. Gives you a lot of confidence for the day when you are high, miles from anywhere and going for it in the clag.