1. Don't run if you're injured. There's no way the body can cope with 26.1 miles if you're not fighting fit.
2. Don't drink/eat anything before or on the run that you haven't tried before. Don't be tempted by energy drinks or gels at the water stations unless you're familiar with them.
3. Don't wear new kit, socks or trainers on the day. Even if it's good kit, it could cause chafing.
4. Don't cut it tight getting to the start. Assume there'll be problems on the train, tube or roads.
5. Don't be surprised if there are very long queues for the loos. There always are.
6. Don't set off too fast. It's much easier on the body to run at a steady pace or even do a negative split.
7. Don't assume you'll find your friends/family easily at the finish. Agree a precise meeting place within a time band.
8. Don't forget to smile as you cross the line! You've made it.
9. Don't be too disappointed if you don't hit your target time. How you'll feel during such a long race is always unpredictable.
10. Don't plan your next marathon until you've enjoyed and reflected on this one!