Bonus Trick on Stage 1 : On Stage 1, exoskeletons will sometimes pop up in the foreground. When this occurs, shoot the skull until a CPU appears. Shoot the CPU quickly and you can receive a bonus (points, shield, more energy, plasma cannon, etc.)!
As soon as John gets in the truck, start shooting the tires. If you
do this you'll make it to Skynet on your first try.