In Trail Blazing, you drive a small, flaming, go-kart through the streets, and must go from checkpoint from checkpoint. You have an incredibly short time limit, but you can add to it by setting things on fire. Hitting a car will give you an extra second, and pedestrians two. If you hit an explosive can or a patch of fire, flames will shoot out and hit multiple targets.
Depending on your strengths and weaknesses, you will need to find your own strategy. Either go as fast as possible and hit whatever you can on the way, or go slightly slower and hit everything you can. If you're playing in co-op, he will sit in the back with infinite moltov cocktails, which he can use to hit patches of pedestrians for massive bonuses.
There are two Trail Blazing missions with 6 levels apiece. I recommend doing this in co-op so you can work towards the "Confidence Men" achievement as well as "Crime Lord".