Method 1: Get a fast car or motorcycle and get on a highway or long road. Drive on the side of the highway you're supposed to be on, dodge traffic or stay in the middle of the lane and just speed and Stunt Points should come in really fast.

Method 2: Go to the Panau Int. Airport and get the sports car at the entrance and drive it to a runway. Once a plane appears, go into the stunt position and use the grappling hook to attach the car to the plane. Once this is done, enter the car. The plane takes off with car in tow. The points begin to rack up quickly. As long as you don't release the grapple from the plane your car will just fly along with the plane.