In reply to The New NickB: Definitely second practising both run then bike and bike then run, or even doing a mini version of the race. I did my first duathlon in April just banking on the fact that I could run and cycle. Legs cramped up on the bike leg and I literally had to force my legs to move on the second run.
Unless you're ultra competitive don't sweat the transitions, and just work out what you're gonna do then make sure you've everything organised. I took a plastic box cos that's what I'd seen on the telly but blue Ikea bags were popular too. It was actually nice to take a little time to get a little rest!