Best advice I got for my first tri was "Race to complete, not to compete." The advice about videos is great, but practice is better. Talk to others, and practice. I

wear on 1 piece tri suit. It makes life a lot easier. A 2 piece is OK too if it's going to be hot, but you will probably need a top, but it could be a trimmed tee. If you do get a 2 piece, you can take off the cycling top and put on a tee with your race number pinned on. Otherwise a number belt makes it easy to put on your # for the run.

I bring a 5 gal bucket and a jug of water in case my feet are sandy after the swim. The bucket makes it easy to carry the stuff to the transition area, and it provides a seat when inverted.

Use a wet suit it the water is cold or if you are a weak swimmer and wetsuits are allowed, but it will slow you T1 time down a bit. It should, however speed your swim enough to make up the difference.

Most important, HAVE FUN!