Assistance. Months in advance I always try to find personal assistants in the country I'm travelling to. This is cheaper (no flight costs) and has the advantage that you then know someone local who can assist in organising travel arrangements and smoothing out any other bureaurocratic problems. It also gives you a great insight into the culture of the country without the usual tourist-local relationship boundaries. The biggest obvious risk is that you don't know the assistant except by email. Ask for as much information as you can beforehand, or for photos. The more you know, the more you can judge what the person is like.

Itinerary. I always make a fairly structured plan of places to be and when, mainly because I have to maintain a strict bowel routine. However, it's good to be impulsive, and things don't always go as you expect (especially in Africa!) so best be prepared for change!

Medication and equipment. Anything you need, from drugs to catheters must either be taken with you, or you must be sure you can purchase it at your destination without prescription.