Accommodation:
After receiving a written quote on the cost of accommodation then making a reservation, make sure you have a copy of any correspondence with you.
Many of the hotels we stayed at in the more rural areas  of Zambia and Tanzania don't bath or hand basin plugs - a bit difficult to have a bath, or rinse out some clothes without one, so take a couple along with you.
Talking about bathrooms - a sound knowledge of how to 'fix' toilets comes in handy in these countries too, as many just don't work, or break down very easily!
All countries:
Don't walk around looking wealthy; leave your expensive jewellery at home; don't flash your money around; don't walk around on your own at night (even the locals don't do that); and respect the culture of the country when taking photos. The Hereros, Masai  and Himbas, in particular, don't like their photos taken except, with the latter two, for payment. Respect their wishes or you could be in big trouble.
Remember, in some African countries the majority of the inhabitants are very poor, have little food and very few possessions which, in turn, creates crime.
Whatever you do, don't exchange your foreign currency on the streets for local currency. You really can be in huge trouble if caught. Nearly every town we stayed in had ATMs and Foreign Exchange facilities - except in Zimbabwe!
Fuel: The price of fuel in Namibia and Tanzania is about the same as in Australia; in Zambia roughly double; and in Zimbabwe usually not available. Remember to fuel up before the border posts to Zimbabwe.
Laundry: Some hotels have a laundry service available, but a tip is to ask the person who cleans the room if she/he knows of anyone who is able to do some washing for you. The answer usually is 'yes', and the cost will be much cheaper. But, negotiate a price first!
Namibia:
Most businesses in Namibia close at midday on Saturday and re-open Monday. About the only ones that stay open are restaurants and the occasional souvenir shop in the main tourist areas of Windhoek, Walvis Bay and Swakopmund.