 Nothing beats being on the trail and trying to train in conditions that are very close or similar to the actual conditions on Mount Kilimanjaro. That means you want to be training at elevation if it's possible and at least understanding how your body reacts at elevation, especially if you never climbed at higher elevation. 8,000 feet, go from mountain that it's 10,000 feet, 12,000 feet and have that initial understanding of how your body reacts at elevation. Try to go for trails with a significant elevation gain.