The general format goes something like this:

Firstly drink some beer, in order to make it seem like a good idea to enter the event. This might not be mandatory but it's how Spud and I have always done it. Prepare by spending the preceding several weeks doing some (but never quite enough) training. 2 weeks before the event, they tell you where it is, which comes in handy. It is generally held somewhere cold, with big hills and lots of rain. Immediately before the event, the realisation sets in that you are not fit enough, so spend lots of money in the bike shop on energy drink mix in the hope it will help. Buying new bits for the bike can also provide handy excuses for poor performance ("I'm not used to these tyres yet.") The friday - drive for hours and hours. You know you've arrived when it's dark, you're surrounded by fit looking people in lycra tights and beanie hats, and everyone has a better bike than you. Register, and mark your map with the 40 or so checkpoints available. Some will be at the bottom of valleys, some at the top of mountains, but as yet you don't know how many will be active or how many points each will be worth. Eat as much food as you can. If there's time, drink some beer too. Go sleep in tent. The saturday - wake up at 6am, take down the tent, pack the rucksacs, tweak the bikes, maybe put on your waterproofs, and ride out to the start area (usually a few miles away). Shortly after the 7 hours have started, you are given a slip of paper that gives the number of points each checkpoint is worth (0 to ~80), and gives a grid reference for the overnight camp area. You need to make up a route that ends at the overnight camp, generating as many points as possible. Ride. Discover the reason the 80 point checkpoint you're riding to is worth 80 points, is because you will almost die trying to reach it. Ride some more. Arrive at the finish and overnight camp area (generally a field or mountain side), and collapse in a heap. Do not be more than 10 minutes late. The penalties increase with time, so that after half an hour you'll have lost most of the day's points. Set up the tent before it gets dark, eat as much food as you can, register for sunday. Beer will be available in cans, but I generally find that the need for sleep takes over at about 7pm. The sunday - wake up at 6am again, eat as much food as you can, fill up with water (often from a stream). Repeat the saturday routine, but with the checkpoints now worth different point values, and only for 5 hours. Arrive at the finish (original start area), and collapse in a heap. Eat as much food as you can, and go and find a pub and a bed!