Common Mistakes People Make in Food Preparation.

Tasting older food to see if it's still good. It's better to be safe
and just throw it out.
Putting cooked meat back on a plate that held raw meat. At
the very least, the plate should be washed with hot water and
soap. Better yet, use a different plate.
Thawing food on the counter.
Washing meat or poultry. This actually may contaminate your
sink and counters.

Letting food cool before putting it in the fridge.
Eating raw dough, cookie dough, cake batter or other foods
with uncooked eggs or uncooked flour
Marinating meat or seafood on the counter.
Using raw meat marinade on cooked food.
Undercooking meat, poultry, seafood or eggs.
Not washing your hands. When in doubt, wash your hands
often and with lots of soapy hot water.