To avoid going over the cliff, or crashing into it, hold down the fire button. The car will now glide around corners at a constant speed, release the fire button to accelerate/slow down. Don't forget that there are still cars to avoid.
To get a highscore without playing the game:
Start a text editor, and load the "highscores" file, and edit it, then resave it. Note that the highscore shouldn't exceed 99,999 and the name musn't be more than 15 characters.
To change the car, load the highscores as above, and use any of these codes (They must be in lower case):
"p911t"-----Porsche 911 Turbo
"vette"--------------Corvette
"lotus"----------Turbo Esprit
"rossa"----Ferrari Testerossa
"counta"--Lamborgini Countach