If you don't plunge the second ball at full speed after locking a ball, you only get a 2-ball multiball and everyone will make fun of you.
Before plunging, bump the plunger and wait for the tachometer lights to settle. Then plunge up the ramp, the ramp will spot a target.
If you get a Jackpot and have all three balls still, shoot then second up the ramp and then shoot Freeways for zero-risk points.