The easiest way of completing the game is to simply go to Shining Hollow as quickly as possible and blow the whole place up with dynamite. If that seems a little bit too easy, then blow up the three radio stations to recruit everyone.
The most valuable people to recruit are Virginia Caygill (great skier), Franco Grazzini (great hang-glider), Amelia Randles (excelent recruiter), and Karl Rudinski and John Stark who are both great drivers.
The best vehicle to get around in is the snow wolf.
If you are going to travel through enemy territory, take a nurse or doctor with you to patch you up when you get injured.