Specifically a well flown TIE swarm.

I know I could build a list with assault missiles etc to try to take them down, but in a more general manner what should I be thinking about in a tourney setting when I have my list that's not optimized to be anti-swarm ?

Real basics: rock placement, ship placement etc.

The other night I got worked badly by the swarm and I want to be able to beat one with just about any list.

Turn zero: you really need your opponent to split his formation, so try to place rocks and your ship in order to force him flying between them. Of course he'll try not to, so it's much easier said then done!

Range control: you want not to be in range of all his swarm at once, so you'd like to get a round on combat with just some of his ships to weaken his alpha strike

Split fire: if he's forced to split his attacks, your chance increase

Beware of blocks!

Step 1: Put a cluster of rocks on the board.

Step 2: Make him fly through those rocks.

Above that, I can't say much because tactics differ so hugely based on the list you're flying (and even the type of swarm you're against). Any specifics you can give us?

6 Ties vs a Big Rey/Fat Poe list.

6 Ties vs a Big Rey/Fat Poe list.

Okay. So at that point, Rey's goal is no longer to get ships in arc; it's to be out of arc. TIEs don't have autothrusters; so Rey's out-of-arc shot is still effective. What's more, TIE fighters are still going to be more efficient than her at just trading shots, so you want to keep that from happening.

Ideally, I would try to bait them with Rey and have Poe come in on the flank. When they go after Rey, use those high-speed maneuvers (and, hopefully, Engine Upgrade) to get out of arc or, failing that, out of range. Look at the Worlds 2014 (I think?) match to see what I'm talking about -- just swap Han for Rey and those Talas for Poe. If Rey slips out of their arcs, Poe can start putting the hurt on; and in the end game, Rey should be able to solo two or three TIEs, even if she's low on health.

In terms of Turn Zero/asteroid placement: you want to make the swarm player have to commit one way or the other, and then punish them for that. To that end, you want some asteroids between you and the swarm; and you want to slow roll as well as you can. Keep Poe and Rey apart from each other, so that your opponent has to broadcast his intentions (if he goes for Poe, just run; if he goes for Rey, run and take turret shots; either way, punish with the other).

If you get actions even when you overlap, then try as much as possible to overlap the swarm's ships. Each overlap is one fewer shot against you, but doesn't limit your own shots because you have plenty of targets. This is the tactic my friend used against me the last time I ran a TIE swarm and it was painful.