On transitions, practice, I don't know how many people I have seen doing their first race looking totally lost and confused in transition (including me my first race). Practice allows you to lay out the things in an order that works for you and develop a system so that there is less chance you will forget something. Also remember it can be crowded on the bike racks so don't practice with your stuff all spread out, you may not have that much room depending on the race.

Race day, make sure to leave yourself enough time to walk through the transitions at least in your head. My first race i didn't do this and and did the whole race exiting and entering transition from the wrong ends, it was really confusing when I exited the bike entrance to go to the run and couldn't find the start of the bike course.

Above all have fun and welcome to the club.