"not too hard really"
i must have been doing it wrong then. :-)
as above, it's not the racing that's the hard bit, it's the trying to stay warm and fed in-between times.
even if you're warm whilst out on the course you can freeze to death during the 'off' laps, take ALL your warm clothes, and then some more, and a big hat, and a sleeping bag to snuggle into while you have some tea and a little bit of food.
and take a big baggy warm jacket that you don't mind getting dirty to wear whilst waiting in the hand-over area, and leave a few pounds in the pockets so the in-coming rider can pick up some tea/food from the catering tent on the way back to base camp.
as for the racing bit, take it easier than full-on race-pace and you'll be fine, and make sure your partner has the same aims as you, do you want to race or just get round?
depending on your lap times you can decide whether to do single laps or doubles, if it's fast there just isn't enough time to recover/eat/mend bikes if you do singles.
but if you do doubles there's always the chance that you'll die halfway round the second lap, or your lights will die. that's all part of the fun.
does your race partner have a Bongo with a huge awning? that's a great help
and draft people on the fireroads