After all, you like all kinds of sports—skiing, hiking, basketball or tennis to name a few, but you don't swim, bike or run at all, or certainly not for more than a few minutes at a time. So how do you start triathlon training without it getting in the way of the other activities that you love?
You need a plan to give you some base fitness in triathlon, or what some would call preparation training. You want this training base so that when the time comes, you can jump into a triathlon training plan without starting from scratch.
Since this is your first one, you're probably considering a sprint triathlon this summer, which is typically 300 to 600 yards of swimming, 10 to 15 miles of cycling and 2 to 3 miles of running.
Given your specific athlete profile—you're fit, just not triathlon fit—it's not that difficult or time consuming to gain some triathlon-specific fitness now. If you do one short workout in each sport each week, you can give yourself a good foundation of triathlon fitness.
The suggestion is to do one swim, one bike ride and one run per week.
Assuming you don't have a heart rate monitor, let's work with rating of perceived exertion and use a scale of 1 to 5. A rating of "1" is easy, "3" is moderate and "5" is all-out sprinting. Make all of your workouts a rating of 1 or 2.
More: Training Zones Explained