Although left-handers make up a large percentage of the world's population – estimates run from 5 to 30 percent -- golf instruction is overwhelmingly aimed at right-handers. Back when good left-handed clubs were hard to get, this was understandable; but that's no longer a problem. Lefties can use computers to "flip" the pictures that make up swing sequences in magazines, but the written instructions pose more of a problem. Fortunately, it's not hard to describe a left-handed swing.
Take your grip. Whether you use an overlapping, interlocking or 10-finger grip is your choice. In all of these grips, your left hand will be lower than your right on the club.
Address the ball. Your feet should be about shoulder width apart. Lean your upper body forward from your hips, with your knees flexed and your weight balanced on the balls of your feet. It should feel "athletic," as if you could easily squat down. Your left shoulder will be slightly lower than your right. For drives hit from a tee, the ball will be placed forward in your stance, just inside your right heel; for most other shots, the ball will be near the center of your stance.
Start your backswing by turning your shoulders to your left. You'll be able to keep your elbows straight but relaxed until your hands are nearly waist high. This is called a "one-piece takeaway" or "keeping the V intact." (The V is the triangle formed by your grip and your shoulder joints.)
Finish your backswing by bending your left elbow. This will bring the club up above your shoulders and simultaneously cock your wrists. Your shoulders will have turned roughly 90 degrees from your address position. The club shaft will be roughly parallel to the ground and pointing over your shoulder, aligned to the right of the target. Your left elbow will move slightly away from your side. Your right heel may lift slightly off the ground and you'll feel some pressure in your left hip and knee because you're resisting the tendency to slide your hips to your left; this is what most people describe as a "weight shift." Keep your upper body more or less centered between your feet. You may have been told to "start your downswing with your lower body." From this position, it will be impossible to start down any other way.
Start your downswing by letting your arms "fall" so your left elbow returns close to your side, just as it was on your backswing, and feel as if you "shift your weight" back to your right side. You do this by simply replanting your right heel on the ground and duplicating that knee flex in both knees that you had at address; there's no big slide to the right. Don't try to do anything with your hands; just hold on to the club at this point. This move drops your hands just below shoulder level without uncocking your wrists.
Hit the ball. You might describe the feel of the bottom half of your downswing in several different ways. Some players feel as if they're making a tennis backhand or flinging a flying disc. Your right elbow will stay close to your right side as your upper body turns to the right, and your left elbow will stay close to your side and straighten out.
Finish your swing. The momentum of the club will pull your upper body around until your chest and stomach face the target. Your hands and club will end up above your right shoulder. Your weight will be primarily on your right leg, and you'll be in a balanced position you can hold easily.