play what you know -make- them play better than others have
Rookie in a tourney....
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Having too many firearms is not an issue.
This depends a bit on your playing strength, but using your online rating (and glancing at a few of your games to give me a guess at how you play), I would recommend that you make sure to do four things:
1. Play "safe" and relatively normal openings in which you can develop normally and fight for control of the center.
2. Make sure to evalute your opponent's threats and avoid losing material by dropping pawns/pieces/exchanges/etc. At more beginner levels of chess, the winner tends to be the one who commits the fewest really bad errors (this is true later on as well, but the errors get more complicated), so try not to do that.
3. Eat/sleep/drink normally. Getting a good night's rest is important, as well as keeping well (but not too well) fed, hydrated, etc.
4. Have fun. If you don't you will play more poorly and be less likely to come back again.
Study tactics! That is the best formula for improvement there is. A good book to start would be 303 tricky chess tactics http://www.amazon.com/Tricky-Chess-Tactics-Fred-Wilson/dp/1580420761 . And that is right I said book. I have found timed tactics on the internet aren't nearly as beneficial to my play as doing problems out of the book, although they don't hurt either. Don't just go through the problems once either. Go through the book multiple times and I guarantee a huge jump in playing strength. After that go check out The Amateurs Mind or How to Reassess your Chess by Jeremy Silman and you should be a rather powerful player.
Vacation is nice when your amount of days to move runs out (this automatically allows us extra time depending on how much time we have saved up). But, some opponents tend to fall asleep (not noticing their time to move has expired 1,2, days etc. or are unable to get to the computer for some reason), then, slip off into a comma for weeks or even months. Other than losing, thats about the only headache on chess.com tournaments... get ready to rent a movie...just joking...Good Luck..
Good sleep is important in chess tournaments 
don't wash or change your clothing or brush your teeth until the tournament. you will smell so bad that your opponents will become distracted and make mistakes.
No matter what I do, I always blunder miserably during tournament games. It's my curse, no matter how hard I study. If I were you, I would do everything in my power to avoid stress! Don't blitz out moves, take your time, and make sure you always consider his side of the board!
Consider every move a blunder, and look for a better one everytime!
I'm attending my first tournament in February as well.
Thanks to all those who have posted with advice.
Here's a thread from late last year where I asked the same thing and had a ton of great advice given to me:
http://www.chess.com/forum/view/general/what-to-expect-in-an-otb-tournament
Some thoughts I'd have for you:
1) Expect it to be a ton of fun and really up your appreciation and intensity for hte game.
2) Don't believe what people say about your online rating minus some points being your OTB playing strength. It's more complicated than that, because it's a different environment, and I believe that most of these formulas really underestimate how much stronger the touranment playing pool really is.
3) Keeping notation in that environment is hard. Practice a lot beforehand if you want to be able to have any chance of recovering your games afterward.
4) Don't resign too quickly, especially at the lower levels. You've got nowhere to go and the next round isn't starting anytime soon. It's not like online where people resign and expect you to resign every time a pawn drops so they can start the next game.
5) If you see your opponent in time trouble, don't try to blitz them. *Use* your advantage to take more time to think and make the game hard for them. Blitzing them just puts you both on the same level, throwing away your advantage.
6) Have a positive attitude and you'll be rewarded with tons of fun!
Play humble but play your best
As a lot of posters have mentioned time is a big factor in OTB play and you need to learn how to use this more effectively.
1. Manage your own time well, as suggested previously depending on the control I make a note of how much time I expect to use / move and budget my time accordingly. However if the position demands it don't be afraid to think
2. Use your opponents time! Just because its not your move doesn't mean you can't be thinking about what your move is going to be! Sometimes your opponent will make an unexpected move in which case you will need to still use your time to think.. but a lot of the time they make a move you have calculated for and in such instances you can use the calculation you made in your opponents time.
3. It doesn't matter if its check mate or your opponent runs out of time its still a win! (well in the vast majority of cases)... as such time is just as much a weapon as your pieces are...
I'm gearing up for my first tournament in late February. Any HELPFUL suggestions from some wily veterans out there? Thanks.