Stay 'on plane'
Every consistent golfer has maintained his or her consistency by staying "on plane" during the swing. There was once a great South African golfer, Bobby Locke, who raided the American circuit with instant success (winning three of the first four tournaments he entered) and a swing that every expert agreed couldn't possibly work.
Locke hooked every shot, not gently but throughly. He appeared to be wildly off-line at the top of his backswing, the clubhead pointing miles to the right. Yet he consistently found every fairway and every green, time after time after time, and then sank the putts. He is famed now as perhaps the greatest putter of all time, but even his putting would have gotten him nowhere without the unbelievable consistency of his shots -- his widely hooked shots -- to the fairways and greens. He won the British Open four times.
The point that has never been noticed about Locke's swing, and which accounted for his consistency, is that it was always "on plane." He simply aimed his whole swing-plane to the right, closed the clubface during impact and swung through regardless.
But how do you stay on plane? That's the question.
To answer it I suggest you get a large hard-cover book and a pen or pencil. Hold the book out in front of you, tilted at an angle. And now swing the pen on the cover as if it were a golf club.
Much that was mysterious before will instantly become clear to you.
When the pen is parallel to the bottom edge of the cover it is also parallel to the top. When it's not, the ends of it point to the side edges.
Think of the swing plane then as an oblong, flat like a book cover. Think of the clubshaft as the pen. Practice swinging with this image in mind. See your plane in the mind's eye before you swing.
Aim it the way you want. And allow it to be flat or upright depending on your build and your swing.
Stay "on plane" and you will become consistency itself.