To fight multiple enemies make sure that you pick one target
in the "edge" of the group. Point your nose slightly off target
so that you don't fly directly at him.

Make sure you have MDTS On.
That helps you with targeting.

Engage Inertia mode, that makes you heat signature much smaller.
Always keep your nose on target.
When in firing range, use Lasers to bring down his shields
and then switch to Guns for maximum hull damage.

You can switch between tageting Engines, Navigation and Weapons with "U" (default).

Continue strafing the target and pick them off one by one.
Remain in Inertia mode and use afterburner if needed to.

Take care of incoming missiles with either dispatching CM:s or using your guns.

Here are some movies displaying different teqniques:

Combat - Mecingo Way (How to fight 10 hostiles)

Combat - Mecingo Way (Combat against multiple enemies in atmosphere)

Combat - Mecingo Way (How to destroy a Capital Ship)