A lot depends on luck, and on how the bomb was detonated. Was it a ground burst? If so, radiation will definitely be a problem. If it was an air burst, with relatively little dirt kicked up, then not so much. And if it was high enough, none at all.

As far as the blast goes, duck-and-cover is it. Get down low, wait for the shock wave to pass, and low-crawl (if practical) to your foxhole or other shelter. The blast wave is roughly 40% of a bomb's energy, if I remember correctly.

Thermal energy is about 30% to 40% of a bomb's energy. Cloud cover will increase the range and effectiveness of the thermal energy. This is why you need to seek shelter after the shock wave passes. Don't look at the fireball for at least five minutes after the detonation.

Ionizing radiation constitutes about 5% of a bomb's energy, and with larger bombs becomes relatively negligible in importance. Nuclear fallout is the primary component if ionizing radiation with a large weapon (above about 50 kilotons).

Tactically, an air burst is of more use, since forces can occupy the affected area faster. Ground bursts extend the area of fallout, but quickly limits the area of blast and thermal damage. Ground bursts would probably be used for missile silos or hardened bunkers, or for a terrorist weapon.

Hope this helps.

Onward and upward,
airforce