I did 24/12 this year as my first 24 solo and the things that stuck in my mind as being important were:
Training - Be uncomfortable, ride when you really don't want to and do as much as you can. If you can drag yourself out for a rainy ride when you don't feel great then you're on to a winner.
Organisation - I didn't have any pit helpers so I made sure I got to the site early and set up my tent right on the track and got all my food, drink and kit set out so I could quickly stop and re-stock. Non-moving time will quickly add up and be prepared for any mechanical or personal gripe.
Eating - Make sure to eat regularly. I made a load of easy to eat sandwiches (soft white rolls) a load of flapjack-type things and had some crisps. I often just grabbed something and ate whilst riding. I made sure I drank most of a bottle of energy drink on a lap too. Gels were good when I got fed up of food. I had a flask of coffee on my table and that was a nice thing to have during the night.
Comfort - As mentioned above, be as comfortable as possible especially how well the bike and clothes fit. If I hadn't been super-comfortable I'd have been in trouble. Although I was soaked to the skin and caked in mud from lap 1 I wore the same clothes for the whole thing and only changed gloves once - a handful of chamois cream every few laps was a welcome treat though!
The night - I felt fine after bed time but looking back I think my body/brain shut down a bit as it was used to being asleep then! Lap times worsened and I had a fall or two. It's worth it to see the first bit of light at dawn though.
Keep going! - Stay happy, keep moving, talk to other riders and enjoy it. At 7 in the morning I was ready to give up and sat down at my tent completely defeated. 20 minutes, a few sandwiches and a coffee later and I told myself that I wasn't going to finish sat in my tent or as a lurker. I pictured taking the chequered flag and cracked on with riding. Racing across the finish line as opposed to just finishing was well worth it.
I only managed 12 laps and 15th place but (apart from my 7am mental breakdown) I actually did enjoy it. A pit helper would have made a huge difference I reckon but I just tell myself I did it super-solo so I'm the bestest!
Sorry, that turned into quite a long post.