How do you protect yourself from gamma radiation?

Protecting yourself from radiation completely depends on what type of radiation (alpha, beta, gamma, x-rays, infra-red, ultra-violet, etc). If you are out on the beach then to protect yourself from the UV radiation, wear clothes or put on sunblock.

Unfortunately this will not help in a nuclear meltdown. Unless you live within 100miles of the nuclear plant then there is minimal risk from any radiation. There might be a 5-10% increase in background radiation, so nothing significant to worry about.

If you are right next to the nuclear plant while it is burning up and releasing radioactive material then get at least few hundred meters away to minimise the exposure viagamma radiation. There may still be a plume of radioactive gases in the air which can irradiate you directly so go downwind. Then the main risk is from airborne radioactive dust which will be invisible and can be breathed in. It can also deposit on the ground and all over you, so no sucking your thumb, and make sure you wash your hands before you eat. If you were to continue to live in the immediate vicinity then food grown in the area would have enhanced radiation and could be deposited in your body.

Basically don't go near it. I'm guessing you are from america as most Japanese will be asleep by now, so you have nothing to worry about. Especially as these plants have not, and will not meltdown.