The two things that make the most difference in your triathlon experience are proper training and proper equipment, both of which will make all the difference in whether or not your triathlon experience a great one. The most important aspect of your triathlon is the training portion. Determine what your weakest sport is then spend most of your time training in that sport. If you are strong with running but weak in swimming devote most of your time to swim training. However, make sure to train in ALL aspects of the race including the transitions. Make training a priority; create a training schedule then follow it!
The most important piece of race equipment is a good pair of running shoes. Running can be very hard on your body so getting a good pair of running shoes is critical. Those shoes will help to protect your joints from much of the impact. When choosing goggles, get a pair that form a nice waterproof seal around your eyes to prevent water leakage and are resistant to coming off accidentally during the swim portion of the race. A bike is next, it really doesn't matter what type of bike it is as long as it fits you well and you enjoy riding it. Last is something comfortable to wear to swim, bike and run in. It is much simpler if it is the same clothing for all three sports. For your transition equipment, you will need a bag to carry all of your race equipment, a plastic bag to cover your things in case it rains, food, water and a towel.
A formal organized triathlon training program that includes every aspect of the event from what to wear and expect, to how to train and transition and all aspects in between can be a great experience. The goal of such programs is to take out as much fear as possible so that athletes can focus on their training, which in turn helps them to enjoy themselves all the more on race day. Let's face it, if it's not fun then what's the point right?