Hi Sven
Guess my experience is a bit out of date but the same sort of princples apply.
First trick is never underestimate how much the body in the other seat contributes. Even more important than car performance is team work. I spent years looking for a good navigator and when I found her I married her.
Second start at local club level and run as many events as possible. It is surprising how even fun road rallies and treasure hunts etc can get you thinking tacticaly early in your career.
Third get hold of, and then bring up to scratch a car from a series a couple of years old or so. I t used to be Datsun 1600s or early lancers but some of the more recent series specials like Suzukis, the AWD Diahatsu Charades etc might be a good starting point.
Finally the only way you ever get good, or like me find out that you are good but not good enough for the ARC, is to enter as many events as you can afford to run. Experience is the key.
Good luck mate you will have a lot of fun.
(And good navigators make great wives)