There are many countries which poses nuclear weapons many among them are enemies who have fought several wars such as Pakistan & India or USA & Russia. So what should you do if your city faces a nuclear attack?
If you were near the site where the nuclear bomb was dropped then you will be killed instantly but if you were far enough or were in an underground bunker then you might survive if you protect yourself from radiation.
The best way to protect yourself from radiation is remain in the place where you are for couple of minutes before moving to a better radio protective shelter. If you are in a poor shelter then wait for 37 minutes at least, before you go out to move to another shelter.
This is because after blast there is a time period when the radiation is at an optimal level, then it reduces. Before going out you should know which is the next best shelter and which is the best route to go there in minimum time?
Best shelter should be underground bunker, with thick concrete walls and no direct window which opens in environment.