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. These mosquitoes bite people to get a blood meal. 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.
Each net costs about $4, lasts for 3-4 years, and protects, on average, two people.
The statistics are well known given the scale of the problem. Every 50-250 nets we put over heads and beds, one child doesn't die.
Every single net matters.