the best months to travel in most parts of africa is usually winter time in europe, that is november, december, january and february, the weather is usually mild and a bit cool in the eastern part of africa
going by your other question, if you are planning on going to Zambia, then I would say August-September, the weather there isn't that bad (maybe around the 30 mark), October/November it gets really hot- 40 plus, then after that is the rain season.