4. You boil when you should simmer.

Result: A hurried-up dish that’s cloudy, tough, or dry.

This is one of the most common kitchen errors. First, let’s clarify what we mean by simmering: A bubble breaks the surface of the liquid every second or two. More vigorous bubbling than that means you've got a boil going. And the difference between the two can ruin a dish.

"I had a friend serve me a beef stew once that gave me a real jaw workout," says Nutrition Editor Kathy Kitchens Downie. "She boiled the meat for 45 minutes instead of simmering it for a couple of hours. She says she just wanted it to get done more quickly. Well, it was 'done,' but meat cooked too quickly in liquid ironically turns out very dry. And tough, really tough."

• Read more about boiling and simmering