Use cockpit view while driving around and regularly through out championships. Best done on long roads on asphalt.
Find a nice long straight road to go back and forth while using the cockpit view. On Ibiza there is a long road going from your caravan towards the middle of the map, down to the casino. When you get to hawaii (Level 10) there is a nice stretch by the airport, use a fast car and go back and forth.
Some races that are difficult I recommend using 3rd person view specially around difficult turns and if you crash and/or spin around switch to 3rd person view to see whats going on.
You can also use the cockpit view through out the island lap (45 minutes) last race in Ibiza, which will gain about 100 kilometers.
I got the achievement with above methods at level 14 (Hawaii). I'm guessing Ive used 60% 3rd person view, 40% cockpit view overall.
Edit: Here's a easy way of gaining miles. video below, get a fast car and floor it.
Video creedit: fundreamer