Here is how to easy get tons of exp.
First you need some shooting skills and plasma/burst weapon.
1.Then you go to desert east(right) from San Francisko and you hunt in real time battle for floaters,centaurs,aliens etc fighting each other.
2. You wait till they hit themselsf, then you choose one of them with low hp(awerness perk is helpfull) and you burst him/plamsa him in eye.
3.Run away. Repeat till you have enought.
I made this way 15k exp in 1hour.