Earning skill points can typically take quite a while, but you can shorten the process significantly. Start by purchasing the Ultima GTR (2012) vehicle. Next, fully upgrade it. Take it to the long stretch on the east end of the highway that runs between Nice and the Horizon festival. Once you are in position, drive northwest along the highway at maximum speed, weaving between traffic and building up multipliers. As you pass through the tunnel and the divider goes away, burn out or use the emergency brake and turn around so that you are now driving in the opposite direction. In this manner, you can build up tons of points in as little as a couple of hours.