1. If You See the Blast, RUN!
The light from a nuclear explosion is seen in outlying areas approximately 10 to 15 seconds before the impact of the blast arrives.
It doesn’t give you much time to work with, of course. That’s why every second counts and preparation is truly key. It’s been a long time since those “duck and cover” bombing drills were a part of the American public school education.
If you’re outdoors or not near a shelter, run and dive as quickly as possible into the best form of shelter in your immediate area.
Please note that windows are likely to implode, so stay away from them. A basement is best if you can get to one. If not, a cast iron bathtub on a ground floor is a relatively safe option. A proper fallout shelter is even better, obviously.
If you can’t get to cover, lie flat on the ground in a ditch or behind any large object that may shield you from the pressure wave.
The scary truth is that it’s most likely going to take several seconds for your mind to process what’s happening. Then there’s getting over the denial. That’s why training is so critical, it enables you to react without thinking.