if you pushed stun jump you should hang from the bottom with a grapple.
Hanging off the actual sides is usually what you do when you've grappled an occupied plane and try to break in (yes, you can mid-air hijack)
You seem to only be able to climb around vehicles that would be occupied by enemies, since those are the only times you'd need to climb around and shoot them off.
Cool things in general are grappling hook related
I've hooked guys to explosives, guys to cars, guys to helicopters, guys to other guys...
I've hooked onto a fuel tank and shot it as I reeled in, causing me to blow back almost as far as I was to begin with.
I always start off exiting the camp by grappling a large rock and parachuting before I get there, slingshotting myself across. My main mode of travel is parachute and grappling the ground to pull myself along.
Either that or sitting on top of a car so I can grapple people to it as we go along.
To unlock new missions/equipment you have to 'clear' areas. Starting camp is easy, there are two things to pickup and one transformer to destroy (that you see immediately)
That's the main trick, it's not just blowing everything up to clear a town, it's also picking up the 'upgrade boxes'.
Oh, and I should say by 'worked out how to get infinite time' I mean 'saw it on the steam forums' >_>
Once you get infinite time going and you can relax and play around with your capabilites you learn more about what you can really do with the game