Remember you can play the ball while driving backwards. With reverse you'll have an early advantage over the forward-thinking AI.
A good tactic is to hold back a little from kick-off to ensure the second hit.

Driving fast will almost always chip the ball.

As for defense if you can, try to pin rival cars against walls, or intercept an incoming ball as quickly as possible.

Earn coins first by completing events in the Academy and winning several tournaments. Then upgrade.

It's better to find a car with balance of power and speed. Shop around for a good mid-sized model. This will provide the best of both worlds when it comes to defending your goal and scoring as well.