Practice swimming a lot. You want to be able to swim the distance very easily. It makes the rest of the race more fun and you wont be questioning why on earth you are paying to torture yourself.

My first tri was fine for the swim. It's the bike that killed me. I kept looking at my legs and wondering why I was pushing myself to make them burn so much. By "pushing" myself, I'm referring to the blazing time of 1:28:52 for 25 miles. Yes, that was over half of my total time, and yes I think that is less than 17MPH.

Basically, just practice what you're weak at.

Also, don't put your bicycle helmet on backwards like my brother did.

Lastly, have fun.

Slow down and have a beer or two in the transitions...... No really slow down in T1 and T2, save the beer for after the race. I have had all of my race problems arise from not following my transition setup and execution plans. Little things such as not having your bike in the right gear to leave T1 can cause you to have the most embarrasing moments doing a tri. Clipped in with no way to turn the pedals because they are in way to large a gear and going over right after the mount line. True story.

Don't wear the t-shirt you get for showing up for packet pick during the race.
Get a number belt.
Wear your tri shorts and top for the whole race, including the swim. Fussing with a dry top on a wet body really cuts into the time.
Learn to change a flat tire.
Carry stuff with you to change a flat. (Although in a sprint, many folks forgo this)
Cross the finish line with a smile, as RV said...don't be one of those folks whose finish photo is of them looking at their watch!
Practice everything before race day.
Have fun.

+1 on the not trying anything new on race day (thats what training is for). make sure your wheels are tight!!

Tons of great stuff here already, just one point I would add that's kind of general but really helped me: be a student! Don't just run, bike and swim, but study the sport! Reading a book like Joe Friels Triathlon Training Bible can make TONS of difference to you.

I can't tell you how many pre-race conversations I have had with people that are TOTALLY unprepared on race day, just because they didn't spend a little time studying the sport!

Also, check the hub page in my sig, I made a one page site on what I wish I knew for my first race.

Good luck!

If you are going to have to go to the bathroom before a race, try to get to the restrooms earlier rather than later. Bathroom lines tend to be really long and nothing is worse than sprinting out of a port-o-potty to the start line.

This video comes to mind... http://www.youtube.com/watch?v=U_6tOzt-nfM

But, seriously, just relax. If you have focused on your training, and done the distances, things are going to come together for you. Are you going to break any world records? Probably not. If you focus on having fun, and enjoying your race, you will. Just relax and let things work for you.

It's easy to get caught-up in the training, speed, power, etc... Remember that we are here to have a great time, get in shape, and represent a great sport.

Take the time to make sure your bike is properly racked according to your race number (if your race does that)
I like to get up early so that I can eat about 3 hours prior to the race, and have some gatorade. I have 1/2 pb&j, 1 cliff bar, an orange and some gatorade usually. Then maybe some cliff shot blocks 30 mins prior with another 4-6oz water.

find somewhere to invest your money. once you do one race, you will want to do a lot more and buy more "stuff." and "stuff" costs cash.

also, spend a lot of time on the bike. learn how to pedal correctly. it makes running that much easier.

1. Don't wear bike shorts to swim. You'll get out of the water feeling like you're wearing a full diaper.
2. Wear a race belt with your number on it. You don't have to worry a about silly pins.
3. Wave and smile to all your fans....or at least your family.
4. Smile and look real cool when you see a camera. The pictures will be available later for you to buy.
5. Learn to punch while swimming.
6. Don't get depressed when you see the number 70 on the calf of the guy blowing by you on the bike.
7. Wear a two-piece tri suit instead of a one-piece. It's easier to pee before the race. You can go behind a tree instead of waiting in the long lines for the porta potty.
8. Learn to pee in the water.

Have a GREAT time!!! Stand by to get totally addicted!!!!

Trisooner, you and I have similar triathlon bladder management strategies.

They will provide bike racks (this was a mystery to me until registration the day before my first tri).

They also provide swim caps, so you don't need to shave your head. I shaved my head for my first one anyway, mostly because I always wanted an excuse to bic it.

Oh, another thing....

Don't carbo load like the world is going to run out of wheat or something. I know too many people that think they need to eat their weight in pasta the night before the race. Eat a sensible, simple, not spicy, not greasy, not garlicy meal the night before. Just eat like you normally do, with perhaps a slight increase in the carb/protein ratio. It's stupid to pound down a massive plate of fettucini alfredo the night before like that's going to make the difference at mile 12 of the bike. That's why we have gels. Having to choke down a few extra calories DURING the race is much better than having to drop a deuce in T2.

Another thing that I did that really helped tie up spme of the loose ends in my mind was to find a race that you are not particpating in and just go and observe if at all possible. Get a spot close to the tranition area and just watch. You will see things that people do that you like and things that you don't. Other than experience, this will really help!

Good Luck

Check out a race similar to the one you will do. It helped me we I was able to say "If they can do it, so can I".

Practice your transitions.

You don't need bike gloves (unless you really need bike gloves).

You won't be the only one who isn't a good swimmer, biker, or runner.

Have fun

Don't do the bike on a mountain bike with big knobby tires like I did. (Hey, my bike was a week old, I figured a bike was a bike...MISTAKE!) Also, make sure you know where to turn on the bike course. I mistook a traffic cop telling a car to turn for him telling ME to turn. Went 2 miles out of the way before I realized the mistake, which meant 4 miles wasted.

Be sure to do at least one brick workout (bike then run) where you push hard on the bike. My legs REALLY were shocked at the transition. (Of course riding on the mountain bike didn't help ;-)

As mentioned, try to not get too caught up in racing. HAVE FUN, and meeting the great group of people all doing what you're doing! Neat experience. Savor.