Preparation:
You're on some high-paying missions. Don't be afraid to invest a little money. It might seem shocking to spend a hundred thousand credits on ammunition for a battle, but if it gets you through, it's worth it.
You need to swat fighters fast, and you don't want to divide your attention while you do it. You don't always have time to aim... and even determining when to fire and when not to can overload your senses.
For this reason, I recommend that unless you're using a fighter, you take a maximum load of launchers. The more launchers you have, the faster your rate of fire. Use the remaining space to buy a maximum load of ammunition. I'm thinking pursuit missiles here. Hunter missiles also work, but take up double the space. Not an option in something mid-sized. Dispersal missiles work, but you'd have to be facing the enemy, which may not always be an option.
The combat:
Once you have a target showing in red on your radar, start firing. You will be holding down the shift key for the remainder of the battle. Don't think about it at all - concentrate on flying defensively, and hammering the enemy with your swivel/turreted primary weapons. You will be holding down the space bar for the remainder of the combat, too. Tap the 'r' key to retarget as often as necessary, but not so often than you distribute your fire among multiple enemies and never actually kill them.
Your missiles will surprise you. Even though you shoot them off at full rate, they will last for the duration of the battle. Adding their destructive power to that of your guns (and your escorts, if necessary) you should find that you make it through.
Good luck, Captain!
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