What To Wear
The most basic thing you can wear is a form fitting swimsuit, then throw on shorts and a jersey for the bike and run. However, there is a triathlon-specific suit most wear that is spandex, has a light chamois (padding in the shorts) and pockets. If the body of water is going to be cold, you need a wetsuit.
A wetsuit is a garment that goes over your swimsuit or triathlon kit and provides thermal insulation and buoyancy. For some races, a wetsuit is not allowed depending on the water temperature. If you plan to wear one during the race, be sure to practice getting it on, swimming in it and taking it off.
Know Your Pace and Distance
Once you have the basic technique down, turn your focus to pace and distance. Building up your distance can also build confidence. If you are training for a sprint with a 500-meter swim, you should be able to swim one and a half times that distance in practice (750 meters) non-continuously. You can do this by swimming sets--a grouping of distances composing part of a workout or drill--at varying paces. Just like training for the bike and run legs, it can help to swim the entire distance two to three times during your training at a moderate pace.
Lastly, you should practice open water swimming four times before your race in a lake or river. The best way to practice is with a buddy or a floatation device for safety.
Preparing for the Race
Study the Swim Start and the Course
Study the swim course, which will be marked with large buoys. The buoys might be different colors or shapes to show where a turn takes place. You should determine what side of the buoys to stay on to stay on course. For example, know if the buoys should be on your left or your right and how many buoys there are before you need to take a turn. The great thing about the swim is that you don't have to stay near the buoys, you just have to go around the key turns.
Second, know the swim start type. There are two major types, a wave start and time trial start. A wave start groups triathletes by gender and age and sends everyone off at once, usually with three minutes between each group and oftentimes called a mass start. This type of beginning often occurs in the water. A time trial start is where triathletes line up and run over a mat every three seconds. It typically starts on land. As a beginner, a time trial start can be less intimidating, but the mass start can be more exciting.
Don't Get Cold Feet
For swim starts that do not begin in the water, find some time to go for a warm up swim. Most triathlons will have a 10-minute designated to warm up. It is important for your safety to swim only when the race officials allow it. Warming up before the race can help get over the initial shock of cold, dingy water.