If your in a group everyone spread out inmediately. If someones struck or gets hit with ground current the others can rush over and perform cpr. Same goes for any potential campsite. Diversify and spreadout.

Okay lets say your stuck out on the trail and a thunderstorm is currently >10 miles away. It is time to make shelter at the lowest local point you can find ASAP. Stay at least 10 feet away from trees but have them be higher than your position in the tent. Get on your sleeping pad and crounch down in an upright fetal position. DO NOT LAY DOWN. You are exposing yourself to the most common cause of lightning fatalities - ground current. By keeping all points of contact "insulated" and close to each other you are best defended from a strike that may happen near you but not directly on you. You are not safe while here. Safer eh barely but at least its something.

Lets say its <10 miles away. The anvil of the cloud is near or above you. You can be struck any time. Move to the lowest spot and do the insulation with the pad and upright fetal position till it passes. Depending on how close it is you may have no choice but to crouch down in the fetal position and wait it out. Covering your head wont help you. Screaming wont lower the risk. I'd probably send a shout out to my boy Zeus and hope I don't get smitten.

Also check out NOAA's informational pages on lightning. I personally spent a lot of time researching after the last big post here on UL and it was useful. Thunderstorms are serious hazards and not taking precautions to gtfo and find substanstial shelter is asking for it.