If you are trying to make a sharp turn, but keep hitting the walls, you can make it easier to turn by pressing L or R (depends on which way you're turning) and/or tap the accelerator quickly. If you are driving a car with bad grip or you're driving on a slippery surface, you can keep from slipping so bad by tapping the accelerator (such action is officially called a Blast Turn by the instruction booklet). This trick also works great for stopping yourself from bouncing between the walls after getting hit or hitting a wall.