Tuck your liquid foundation away and replace it with a tinted moisturizer that has a sunscreen of at least an SPF 30. This way you won't feel completely naked without your foundation and you'll be protecting your skin from the sun as well. Choose a tinted moisturizer that is also water-resistant to keep you looking lovely even if you're splashed by the pool.
Sweep a little bronzer on your face to give your skin a natural glow if your skin tends to be pale even when in the sun. Don't over do it; bronzer isn't a substitute for a natural or even spray-on tan. Apply it lightly on those spots where the sun would normally kiss your face with color, such as your cheeks, nose and forehead. If you have a darker skin tone or you've already got that summer tan, use a soft blush that isn't too harsh or loud on your skin. This will work to give your cheeks a healthy summer glow.
Create a soft eye. Liquid and pencil eyeliners don't hold up well in the sun and can give you a smudgy look. To avoid raccoon eyes, either skip the eyeliner for a natural unlined look or use an eyeliner brush to line your eyes with your eye shadow instead. This creates a softer look that won't run in the sun.
Wear neutral eye shadows that are close to your natural skin color. Apply a primer beforehand so that your shadows will stay put and won't crease or melt under the sun.
Toss your black mascara and apply a brown-black to your lashes instead. Make certain that it's waterproof so that it can handle any water play, and apply it sparingly.
Use a tinted lip gloss and pass on dark, overly bright or heavy lipsticks. Protect your lips first by applying a moisturizing lip balm with a sun block (SPF 30 or higher) to your lips before adding that pop of sheer color to your pout.