I've read a lot of other people's combat strategies and I will admit, those are for braver people. I tend to fight methodically, which often means slow and stealthy. With the practice, I've actually found playing on Heroic Mode now to be easier than the first time I played on Normal. I'm not the best at FPSs (a supreme understatement), so these strategies are really for my brothers and sisters that just don't have the knack for this kind of thing but still want to play.
Don't waste ammo trying to hit them head on. Strafe and let them pass, then take some shots with whatever you've got handy once you see the driver. If you move in the same direction the Ghost is turning, you'll have even more time to pop a couple in the driver. Unless you've got excellent aim tossing grenades, don't waste them. Like Shades, flipping vacant Ghosts is a good way of covering your ass.