I have been pacing at my local parkrun, which has been providing pacers for the last year. In my experience the best way is pace according to the terrain. Keep the intensity the same, but slow down (a little) on the hilly bits. Make up time on the flat. You can afford to be 10-15 seconds down over the first km as it allows people trying for a pb to keep in touch (being 10 seconds ahead of schedule at 1k is a recipe for running on your own for the next 4k). I usually aim to make up the deficit over the next 4k to finish on schedule.
Don't be discouraged if a lot of your group fall behind as many of them will be overambitious in choosing a pacer to run with. I often have people wanting to run a new pb by over 2 minutes.
Kattefjaes, you seem to be under the mistaken impression that it is only the beginners or slower runners that are performing outside their comfort zone. It's the same up the front with the faster runners too.
Literatin, perhaps I haven't got the exact phrasing used, but the general idea that it's only 5k you don't need water is correct. In the few times I've been at Edinburgh parkrun I have gotten the impression that the guy is indeed a bit of a twat (but perhaps I just haven't warmed to him).
Jeez people don't get your knickers in a twist, I was paraphrasing and they may not be the exact words used. Nobody was picked on, the water bottle is retreived and it's all taken in the lighthearted manner in which it is intended. I think that the point which is trying to be made is about trying to run without your emotional safety blanket and see how you get on.
The prerace briefing at Edinburgh parkrun always amuses me. At some point the race director asks if anyone is runnning with a water bottle, followed by a few sheepish hands going up. He then asks if he can get a closer look at someone's bottle. When the unlucky parkrunner hands it over he throws it over the fence into the field next door saying 'you don't need that nonesense it's only 5k'. A point well made.