From Liz in Ghana:

1. Plan for a 15 hour trip; expect the bus to leave 2-4 hours late.

2. Dress for the air con. During the day, the air conditioning will be sufficient from keeping the bus from getting unbearably warm. At night, the air conditioning will be sufficient to cause hypothermia in penguins.

3. Bring ear plugs or headphones. Or learn to love very loud Nigerian movies. 

4. Plan what you eat and drink around rest stops.  The bus will usually stop 3 times, each stop about 4 hours apart.  The restrooms get progressively worse as you go north. 

5. Lean back. Avoid sitting in front of a grumpy lady who hits you on the head every time you try to recline an inch, despite the fact that her chair is in the lap of the person behind her. 

6. Make it a party. Your "friend" calls to tell you he's having a steak dinner with a glass of bourbon? I've got a 1.5L water bottle of gin and juice, and bag of popcorn, so there!