Hit and run
Associated movies
Moving around at will, use 'hit and run' tactics to whittle down the enemy bit by bit. With such an intricate maze of rocks, there's excellent potential for this sort of thing, and I've had quite a lot of fun with it. Battles can be relatively long, depending on how much moving around you like to do.
Of course, there are places which are relatively good hold-out points, particularly bottlenecks, and you can enjoy some hold-out work if you want. But it can be hazardous letting covies build up, and in certain spots you can be in danger of getting surrounded; so you might want to get moving before too long!
Getting established
When you start exploring the hit and run idea, you may at first find it hard to get established in the rocks at all, as the covies can be quickly upon you, setting your shield bleeping in seconds - and that's if it's not already bleeping from your entry drive! But you should be able to find particular ways to do it, to get a bit of initial breathing space. It depends on the covie layout of course, with the particular set-up you're using.
Weaponry thoughts
In regard to weaponry, you have lots of possibilities to enjoy. Plasma weapons are strong choices for fast close-quarter work in the rocks, but then there's the enjoyably visceral feel of the AR too. It's less powerful though, and trying to tackle things with just an AR would likely make a tough challenge on Heroic. Coupling it with a pistol makes for a nice combo, and you can see an example of that pairing in BCM629.
If you don't have an AR on entry, there may be some dropped by killed Marines. There are also supplies at the lifeboat of course, but it would be hard to grab anything at the start, due to all the covies nearby.
Don't overlook the possibility of using a sniper rifle. It can be a lot of fun moving around getting sneaky shots from a safe distance, picking off covies a few at a time. It gives quite a different type of experience to the more usual close-range business. If you don't enter with a sniper rifle, there's one at the lifeboat (along with spare ammo) and there's also one which may've been dropped by a Marine, a source I use in BCM629.
Marine considerations
Incidentally, for hit and run it's probably best to have either no Marines around or very few, otherwise the covies can get significantly distracted by them, taking pressure off you.