The key to scoring well in golf is being able to predict where your ball will land when you hit it. Obviously, the more repeatable your swing is, the easier this act of prediction becomes. But if you clutter your mind with too many swing thoughts, you'll struggle to develop any consistency. You only need to focus on a handful of basics; then the rest of your swing will happen automatically. The secret to a consistent golf swing is to know what those basics are.
Address includes your grip, balance and alignment. There is no one correct grip but whichever grip you choose, you need to make sure your hand positions are the same each time. Balance is a matter of posture and relaxation. You gently flex your knees, bend from your hips and let your arms hang straight down; your weight should feel as if it's over the balls of your feet. And alignment simply means that if lines were drawn through your shoulders, hips, knees and feet, they would all point in the same direction. A consistent address makes your swing more repeatable.
The one-piece takeaway is one of the most poorly explained concepts in golf. Many people believe it means you lock your arms straight out as you start your backswing. Actually, your arms remain relaxed; a good one-piece takeaway means you turned your shoulders to start your backswing. If you turn your shoulders, your arms can remain fairly straight but relaxed until your hands are about waist high. From there you simply bend your right elbow (if you're right-handed) to finish your backswing. This is an easily repeated motion.
Many players move too much during their downswing. A good weight shift keeps your weight between your feet. Imagine a vertical line extending upward from halfway between your feet. When you turn your shoulders to your right during the backswing, you don't need to slide your hips sideways because more of your weight moves to the right side of that line. Likewise, when you turn to your left during the downswing, more of your weight moves to the left side of the line. Eliminate the excess hip slides. Your balance will be better and your swing will be easier to repeat.
Rhythm is the most overlooked aspect of a consistent swing. Researcher John Novosel found that the backswings of most professional players (both male and female) were about three times longer than their downswing. It didn't matter whether you were timing Bobby Jones or Nancy Lopez or Tiger Woods. And because most players can easily count from one to four, this three-to-one relationship makes it much simpler to create consistency in your swing rhythm.