If a bomb goes off, don't look at the blast, go to an area in your house without windows and little air access, close the doors and wait there for 24 hours.
Ideally, it's a closed basement surrounded by ground and concrete. If not, maybe a bathroom wine cellar, etc. the idea is to isolate yourself from the surrounding radiation in the air.
Hopefully, you have a shortwave radio with fresh batteries or one you can hand crank. Because cellphones and access to information will be limited, the shortwave radio is important because ideally, city officials will be broadcasting where to avoid going outside and safety instructions.
Don't go outside within the first 24 hours, as small radiation particles will fall on you and cause serious health issues.
If you do go outside get rid of all your clothes and take a shower, don't use conditioner which binds radioactive material to your body.
They say that after 24 hours, radiation levels should drop off significantly, since the winds will hopefully blow them away. But that's why a shortwave radio is important to have, so you know which directions of the city are getting the radiation.