Make sure they are well broken-in before the event by wearing them on practice walks. All walks should include some hill work and rough cross-country sections. Remember that very hilly routes will obviously take more time and energy than comparatively flat ones. By the end of the training period, you should feel able to walk for 10-11 hours without difficulty. Remember to drink sufficient water.
Dehydration is a real risk and can result in death or serious injury.
Always take maps and learn how to use them together with a simple compass. As part of your training, choose a weekend to practice night-walking. Distances, terrain and direction are all very different in the dark, and walking rough ground by torchlight is a skill that needs to be practiced. Estimate which areas of the Trail you will be walking at night and practice them. Two weekends before the event try walking about 8-10 hours on both Saturday and Sunday.