Hold R1 to lock on to an Endo. Then, hold L1 to switch to first-person mode. Your target will move from the torso to the head, requiring fewer hits to kill. Then, pick up the head for Skytech Points. This will not work well if the Endo is moving.
Destroying Skynet Tanks
If you encounter a Skynet Tank, do not waste rockets on its powerful armor. Instead, use this trick to take out all the parts. Your best chance is to take out its guns first, then searchlights. Then, find C4 to blow up the tracks to destroy them. Be careful where you place it -- the tank can burn you with its flame gun.
Destroying Skynet Planes
This is one of the toughest enemies. to hit. Destroy the plane by firing a R6 rocket at one of its weak spots. Do this by dodging the rapid lasers, then hit the engines that allows it to fly in the air. Repeat this process until the plane has been shot down. Watch out for more cyborgs dropping from the plane.