2k swim, 90k bike, 21k run
Well the basics are like what Arthur Lydiard devised in the 50s and 60s to produce multiple gold medalists and world record holders in the form of Snell, Halberg, Magee and Baillie etc etc….
What you need to do is to build up the stamina and strength to complete the distances. And remember it is a triathlon, not a swim race, bike race or run race. If you have not trained enough on the bike it does not matter how good a runner you are, you will not be able to run to your potential if you are not fit on the bike.
The swim is made up of approximately 1 stroke every meter of swimming so approximately 2000 strokes. In order to be able to do this on race day you need to show your body what it is like to swim 2000 strokes, so at least once per week you should build up to swimming a main set of 2000 strokes. One of my favorites for developing athletes is 10x200m on 20sec rest done all as Pull (pull = paddles + pull buoy)
The cycle consists of 90 kilometers. Again you need to build the strength and endurance to be able to complete the ride so you can get off and run. This involves a longer ride each week, and then several shorter rides focusing on building strength. For example another favorite of mine for developing athletes is simply to jump on the Turbo or indoor trainer, and do a 10min wup/dwn and 15x1min in a big gear at a very strong intensity. So you get nearly an hour worth of aerobic work and build strength at the same time.
You can check out the rest of the article here http://www.debihazelden.co.nz/what-does-a-beginner-need-to-complete-a-half-ironman/