Do as many tricks as possible to earn boost. And boosts will get you the furthermost possible.
Do flips by holding the screen, or do wheelies by tapping the screen to stay on your rear wheels – both of these tricks earn you boost.
Also you can do big air and perfect landings for more boosts.
When landing make sure to swipe down when your vehicle is in a good landing position to earn a boost.
Each car is rated with stars and, obviously, cars with 5 star are the rarest and the better ones. Try to those as much as you can.