Plug your strobe light into a power source and position it off-camera, pointing at your subject. Cover the lens with a blue gel.
Turn the strobe light on. Some models have a power switch or button, usually located at the back, while others turn on as soon as they are plugged in. If this is the case with your strobe light, use a power strip with an on/off switch for easier operation.
Turn the strobe speed dial rapidly. Turning it to the left slows the flash rate while turning it to the right increases the speed. Experiment with different rates and directions of rotation until you get the effect you want.
Turn the strobe light off again as soon as possible. The light should not be on for more than a couple of seconds at most, unless you are simulating an unusually high number of lightning strikes in quick succession.
Add thunder sound effects in post-production. If for some reason this is unfeasible, strike a thunder sheet off camera a few seconds after the lighting flash.