How will the weather be?
Weather varies widely between Southern and East Africa, and it’s worth researching the countries you intend to visit. Winter in Southern Africa is from June to August and it can be very chilly at night. Winter is dry season which generally offers better game viewing opportunities as the animals tend to gather around the water holes, so bear this in mind when planning. Even during dry season, rainfall can be unpredictable so do be sure to pack in a rain coat.
A good weather summation of Africa is given on Wikipedia, including a precipitation map.