Take a diesel-engined vehicle. Diesel is more easily obtainable, and generally cheaper. Fuel economy is generally better as well, so the vehicle's range is increased.
Ensure that the vehicle has independent fuel tanks, so that should one become damaged, it is possible to use the others - not as easy with diesel as with petrol.
Ensure that the vehicle has a fuel capacity for at least 1000 km.
Take a full toolkit, with all the necessary tools required for the vehicle.
Take plenty of spares and repair supplies (including wire, bolts, gasket tape, welding rods, etc).
Take a minimum of three jacks if using leaf springs.
Take a GPS.
Allow for a multitude of spellings of place-names. Pairs such as Yabelo or Yavello, or Nekempte or Neqept are all common.
Ask locals to confirm route, in sign language if necessary - there are no signposts.
When asking directions from locals, try many different pronunciations - it is not only their spelling that is non-standard, one person may pronounce a name one way, such that if you repeat it faithfully in the next village, you will get a blank look. For example "Gore" was pronounced "Gor" or "Gorey - people who used one, couldn’t recognize the other.
Take a good supply of drinking water, and a filter or other water-purification system. No "clean" water was available, even in Addis Ababa.
Take an adequate supply of tinned food, since none is available outside of a few shops in Addis Ababa, and fresh food does not keep long.
Drive slowly, and don't expect to cover more than 300 km per day at best in Ethiopia.
On tar watch the side of road to spot potholes - people drive onto the shoulder to drive round the potholes (also works in Zambia and Kenya). This is often more reliable for trying to spot potholes at a distance.
In Ethiopia, don’t drive in other vehicle's wheel tracks - while this is sound advice to the south, in Ethiopia, the odds are that the vehicle will be a large truck, with a higher clearance than even a 4x4. This means that you will regularly hit rocks.
Don't expect facilities at camp sites - or even campsites. It is usually possible to camp at government hotels, but camping facilities are only provided at Lake Langano.
Take of cash or travellers cheques - don't rely on credit cards or transfers from overseas.
Change money "legally" in Ethiopia. Only consider using the black-market if entering Ethiopia on weekend - otherwise the banks are cheaper.
An Ethiopian trip: 27/11/1999 to 17/01/2000Giles Mulholland 31 January 2000