Don't sweat the meta-gaming, power-gaming, cheese-weaseling, and/or munchkin tactics. You will see a lot of it in LG. That doesn't mean you can't have fun.
The most important thing, I think, is to be mindful of the pace of the adventure. Don't let the party waste time if there's not "free" time to be wasted. LG is all about *finishing* the adventure, so PCs can get the xp, gold, and (most importantly) item access. If they don't finish, because you let them spend a hour role-playing out a cool scene, players will whine.
Now, sometimes an RPGA mod *requires* some extensive role-playing (as opposed to just rolling dice). Sometimes, players itching to get to the next combat will fidget, whine, and complain that they're wasting time. But you're the DM, you've read the adventure, you know if this is time they are free to "waste" with extensive role play.
Some of the best RPGA judges I have had, have been people who allowed a lot of role-play, but knew when to "move it along." Also, they knew when to finish out a combat round by round, versus when to "hand wave" it and move the party on because they were demolishing the opposition.
Finally, be very clear (to the point of meta-gaming) about actions that will get PCs taken out of the campaign (either temporarily or permanently). I usually give a subtle hint ("You suddenly remember that the captain of the guard told you not to hurt anyone"), then a not-so-subtle hint ("hurting someone would be bad; killing someone--even in self-defense--will probably get you in jail and maybe even executed"), and end with a blatant out-of-game warning ("If you do this, your PC will be arrested, tried, convicted, executed"). If the player persists, so be it. They can't say they weren't warned. Most mods will not have situations like this, but a few do (because of where they take place, the NPCs involved in that story, etc.)
Now, having said all that, have fun! I have met a lot of great people through the RPGA, and played a lot of great "slots" at cons (big and small) and home gamedays. A good DM can even make a bad module great fun!
Also, Yeovil Andy's advice to "get involved" is very good. To more you know your region, and work within, the more fun you'll have.