From a old US Army handbook I read (not going to be exact wording but close enough)
Find the nearest ditch preferably 2.5ft wide 4-5ft deep cover with a mistress or anything as thick. Wait for the explosion and count to 30 seconds. Climb out of the hole run away from mushroom cloud. You have 5 minutes to get 1 mile. 10 minutes to get 5 miles. At which point vehicles may be an option if powered off at time of explosion. Now get 10 miles away in 15 minutes. (You want generally be 15 miles away to be at least risk for radiation exposure.)
