Not really. The only preparation that matters is preventing it from happening in the first place. Should one go off, all bets are off depending on various factors: airburst/surface, type of material, winds, etc.
I've had some pretty interesting conversations with people in the nuclear field, including many from one of the homes of the Manhattan Project; Oak Ridge, TN. With many of the players in the radiation/nuclear field locally, there is lots of information and perspectives, but the consensus is generally that prevention is best hope.
If anyone wants to see what the effect of a detonation on their area, here's a reference site: NukeMap