Charging bunch of enemies will harm you so you better have a simple little med kit to heal your wound's.
About med kits - 5 is enough to heal almost every single injury.
Remember to pick up every single item you can find - it might help in future to obtain a key from a strange monkey that just happens to be in that strange laboratory that you've just enter, because that mad scientist capture your girlfriend and wants to turn her into...

As a soldier you will be teached to pilot tank, truck, chopper, battlemech, aliens war machines and use every single weapon in the world (and universe). And they will teach you that in under 30 minutes!

As long as the vehicle has weapons, it doesn't need fuel to drive.
A knife stab does more damage than a burst of 9x19mm bullets.
It's always awesome to pump a shotgun, even if it has a self-repeating semi-auto mode.

Oh my... If I'd tried to list all of the little lessons learned while playing strategy games I'd spam this forum to full capacity of server quota. ;]

So I see you've played EVE Online, then? ;)