How can you prevent lead poisoning?

Avoid exposure. The best prevention is avoidance of exposure. If you can stay away from that, that's the best way to prevent poisoning. If you must be in the environment where the exposure is inevitable, you want to use protective wear (respirators/masks) and special outfits that may protect your skin, upper respiratory tract, eyes etc. Also, showering after such exposure may remove lead particles somewhat.
Prevent plumbism. Children are exposed mostly from lead paint which is flaking from walls. They may ingest the chips. They are also exposed when they play in soil that is contaminated with lead, when they bring their hand to their mouths. Clean up chipping paint, have home inspected for lead and remove it. Adults are often exposed removing lead paint from interior walls. Always wear a mask or ventilator.