Check the local weather forecast before starting your work. If you see threatening clouds, use the "30-30 rule". If the time delay between seeing the flash of lightning and hearing the bang of thunder is less than 30 seconds, begin moving toward a sheltered location. Lightning can strike before or after a visible storm.
In an open field, seek a low spot for shelter. Seek shelter away from hilltops, trees and utility lines. Seeking shelter in a closed building is safest. Do not use items connected to electricity or plumbing. A vehicle with the windows rolled up is the next best thing; this includes tractors with a cab.
Stay in safe shelter at least 30-minutes after you hear the last sound of thunder.