I did one a couple years ago (5K-20K-5K) and might do it again in June if my running injury is healed by then. The best advice I can give -- and which I'll follow myself this time! -- is to pace yourself over the entire event and not just by segment. Basically, my mistake was that I ran the first 5K as if it were a 5K race, then the 20K bike route again like it was its own race, and then in the final 5K I had nothing left. I actually did OK, but probably could have won my AG if I'd had any gas left in the tank for the 3rd segment.

So think about the overall distance and plan your pacing accordingly. And yes, that final bike-to-run transition is a real *****!