The Easiest and fastest way to get skill points in Forza Horizon 3, is probably the west side of the map. You can collect about 300 thousand skill points (That’s 3 points to spend in the skill menu) in about 4 minutes.
Try to stay under 150 km/h / 100 mph and use drifts to string your way back and forth across this area. The best part about this spot is that there are almost no trees or stones in the way of you combos.
The only way that can stop your skill point bonus is a bad landing, but if you keep your speed moderate, you can stay here indefinitely and get as many skill points as you want in no time.