If your planning to go on Safari in South Africa, you need to take precautions against contracting Malaria. The first step is to take a course of anti-malarial drugs. These will typically be taken a few weeks prior to travel, throughout the duration of your trip and for several weeks after you return home. You can get some brands over the counter but others require prescription. Consult your GP well in advance of travelling to ensure you have the correct anti-malarials for you, as well as any other vaccinations you may need.
Travelling in the dry season ensures a minimum of contact with mosquitoes as they breed in standing water, which is less abundant during this time. Happily, the dry season is the best time to see big game as vegetation is low and animals congregate at water holes. Mosquitoes are most active in the evenings, so cover up as much as possible and wear insect repellent as the anti-malaria drugs are not 100% effective. If you are sleeping in an unscreened area, use an insecticide impregnated mosquito net at all times.