The most effective means of preventing malaria is sleeping under a mosquito net, specifically a long-lasting insecticide treated net (LLIN).
 
Malaria is transmitted by certain mosquitoes when they bite. The malaria parasite then passes from the infected mosquito to the person being bitten. They typically bite between 10 o'clock at night and two in the morning - and that's one of the most important things we have on our side: if we can protect people in affected areas when they sleep at night we have a very good chance of preventing them contracting malaria