Swimming is a drag—literally. The more water your body pulls along with it, the longer it will take you to get from one end of the pool to the other. Lucky for you, even the slightest adjustment in form can deliver huge returns in efficiency, says Emmett Hines, a masters swim coach who leads swim camps across the country and author of Fitness Swimming. Accelerate your pool learning curve with these freestyle swimming tips from Hines. —Alyssa Shaffer Keep your head down. At no time—even when taking a breath—should more than one-fourth of your head be above water. Toe…