My FLGS is currently running a two-week Team Epic tourney (400 points, must include at least one Epic ship). They've done this a few times, but there are a few common errors that seem to come up a lot that are worth noting:
1) Epic ships are SLOW. The fastest epic ship without an Engine Booster will only be moving an amount equal to a small ship doing a 3-straight, or a large ship doing a 2-straight. Keep that in mind when you plan your deployment. If your huge ship is going to take 4 rounds to get into the fight, and the rest of your squad will be there in two, then that's a heavy point advantage for your opponent during those first few rounds. This is especially crucial if you're playing against a time-limit.
2) Know how damage works. The Vader Raider is popular, but one thing that isn't as commonly noted is the way the damage works. According to the damage rules, when a huge ship suffers damage that does not explicitly affect a single section, then the opposing player gets to choose where that damage comes from. I'll confess that I had overlooked this particular rule the first couple of times I entered a tourney like this.
3) Have a plan for energy management. Sure, it may seem neat to have a Comms Booster, and three energy weapons on Hardpoints, but you're going to be on fumes within a few rounds. Consider leaving a hardpoint empty or use energy-efficient weapons like Quad Lasers. Alternately, make sure to bring the Tibanna Gas Supplies.
Any others that I'm missing? Beyond the smart-alecky answer of "Don't use epic ships?"