Coins can be earned by completing the video ads within the in-game store (500 per ad) or connecting the game to your Facebook account to enable multiplayer mode.
Increasing speed
Finish tricks or long jumps with perfect landings to get an extra boost for your truck. Lean your truck forward into the tail end of a jump. Slam the brakes before a big jump.
Stars
Earn stars from different stage separately instead of collecting them all at the same time. It may be difficult to get all the stars available in a specific stage by completing all the tasks during a single race. Because of the large number of stages, it is better to race them all for stars. Each star will be counted equally, whether from completing a race within a time limit or doing a certain number of flips.