Food safety experts recommend thawing foods in the refrigerator or the
microwave oven or putting the package in a water-tight plastic bag
submerged in cold water and changing the water every 30 minutes.
Changing the water ensures that the food is kept cold, an important
factor for slowing bacterial growth that may occur on the outer thawed
portions while the inner areas are still thawing.
When microwaving, follow package directions. Leave about 2 inches (about 5 centimeters) between the food and the inside surface of the microwave to allow heat to circulate. Smaller items will defrost more evenly than larger pieces of food. Foods defrosted in the microwave oven should be cooked immediately after thawing.
Do not thaw meat, poultry and fish products on the counter or in the sink without cold water; bacteria can multiply rapidly at room temperature.
Source: Excerpted from FDA Consumer, November 1996 update: Can Your Kitchen Pass the Food Safety Test?