With summer practically here families are spending more time at the beach or pool and that means you'll need to keep plenty of sunscreen handy.

But doctors say many of us are making mistakes when when it comes to applying it.

Dermatologist Melissa Piliang says, "You must put on 1 ounce of sunscreen, that's the amount in a shot glass, to cover your whole body. Most people don't put on that much."

Skimping on sunscreen is one of the most common mistakes people make. That "slip-up" leaves you far more likely to get burned.

"If you're putting it on too thin, you're not getting an SPF 30, you're getting more like an SPF 10, so sometimes it's easier to put on a higher potency to get you to 30, but you want to put on a nice, thick coat," says Dr. Piliang.

Another sunscreen "slip-up" is waiting to apply it until you're already at the pool. Putting it on 10 to 15 minutes before you go outside gives it a chance to be absorbed into your skin.

The American Academy of Dermatology recommends choosing a sunscreen that is SPF 30 or higher. And it says choose one labeled "broad spectrum" to protect against UVA and UVB rays.

Another common "slip-up" is skipping the re-application.

Sunscreen should be re-applied at least every two hours, especially if you are swimming or sweating.

Experts say be sure to choose a type of sunscreen you will actually use. Many people prefer a spray because it's quick and you don't need to rub it in.