This is my first year doing the Tri thing, but I did two this year and learned some valuable things.

1. If you're not worried about time, just wear under armor on the swim (and a wetsuit if they require it). At the first transition, change into your padded bike shorts. At the second transition, change out of your padded bike shorts. A lot of people swim and run with their bike shorts on, but if you're not worried about adding 30 seconds on to your time, it's well worth it to be more comfortable during the run (and a lot more comfortable during the whole race because you won't have soggy shorts the whole time).

2. To echo what Mr. Jim said, practice your transitions. It's not only good to practice changing all your clothes, but it really helps to run after you bike, or bike after you swim, because you need to know how it affects your body to not be starting your bike/run fresh.

3. Make sure your wetsuit fits, and if it's too tight cut off the arms. If they don't require a wetsuit, don't wear one. There's nothing worse than a wetsuit that's too small, because it takes all your energy just to get your arms above your head. As you might have guessed, this is spoken from experience.

4. Again, with the transition practice, start a list now of things you'll need so you can add to it when you think of new things. It seems like there is always someone near me in the transition area that forgot something rather important. To go along with this, when you're actually preparing for the race, gather all your stuff in a big bucket. Then, at the transition area, lay all your stuff out on your towel (in order if you want) and then flip the bucket over so you have a seat to change shoes and socks. There's nothing better then coming out of the swim and not having to sit on the ground to put on your biking shoes.

5. Make sure you have EVERYTHING you need to change a flat. I know it's rare, but I got a flat in my first tri, and I had to walk/run half of the bike course with my bike by my side. Needless to say, it more or less ruined the race for me.

6. If you're not worried about time, take everything you need to be comfortable on all stages of the race. Wear sunglasses and gloves on the bike. Take your camelbak if you drink a lot. Don't worry too much about transition time or aerodynamics or anything. Chances are, the race with have you wear chips that will track your time. This way you can see your times for all three stages, and you can just ignore the transition time.

I'm no expert, but I figured I'm the type of guy who doesn't care too much about my time either, so I thought these thoughts might help. Good luck. I hope you enjoy it as much as I have.