Get to full speed (preferably but not necessary) and press [N] for neutral. Now you can cruise along at full speed with easy steering and invulnerability. As long as you stay in neutral you will have unlimited time as well.
Another trick is to repeatedly hit the 4 key (4th gear) until theprogram has an error. Continue with the right mouse button. Repeat until you get a high score.
Try hitting the cow for a surprise!