Triathlon is a confusing and tremendously complex sport. From training plans to gear selection to race strategy, there are a thousand variables and million ways to put them together.
One of the most difficult parts of triathlon is assembling your best race to get yourself across the finish line in the least amount of time. I wish there was a simple answer to this, but the solution is so dependent on who you are as an athlete.
If you're strong swim/biker, but a weak runner
There are two strategies you can pursue:
1. Saving it for the run.
Since you have a very good swim and bike, you can afford to dial back you effort on those two legs and still be relatively near the front of your race at the start of the run. By being a little more conservative in the first two sports, you will be (relatively) fresh starting the run.
2. Putting all of your eggs in the swim/bike basket.
This is a bit like a kamikaze mission. You swim and bike very near your maximum capacity and then hold on for dear life on the run. This is a very painful way to race, and has a high probability of blowing up on the run. But it has worked for me several times.
If you're a strong lifelong runner, okay cyclist, poor swimmer...
Limit swim/bike losses. You have the running experience so that almost no amount of fatigue will slow down your running more than a small percent off your fresh capacity. By putting a lot of effort into the first two stages of the race, you can limit how much time you lose to faster swimmers and bikers. Then, because you're closer to the front of the race, you can use your fatigued, but strong run to reel in weaker runners.
If you're a good swimmer, weak cyclist, and weak runner...
Save your energy for the bike/run. The swim is so relatively short that even phenomenal swimmers can usually only gain a small amount of time on weaker swimmers. As a good swimmer, you can dial back your intensity on the swim and not slow down very much at all.
If you're a weak swimmer, strong cyclist, weak runner...
Survive the swim. After that, put a lot of effort into the bike to limit the damage competitors did to you on the swim and will do on the run.
Don't be afraid to experiment with your race plans or to fail occasionally. It's only then that you can identify your weaknesses as an athlete.