LINE UP YOUR LEFT HIP AND LEFT FOOT
I constantly monitor my swing to make sure it's ready to compete at the highest level. I tend to spray it and lose speed when I overturn my hips or shift my weight to my left heel instead of to my left big toe on my downswing. To fix this, I'll swing in front of a mirror and stop in my release position. Although I believe your release is something that "happens," not something you make happen, this test reveals the quality of the moves that preceded it.
If my left hip is ahead of the instep of my left foot, I've swung out of sync and have shifted too much weight to my left heel instead of my left big toe.
If my left hip is in line with my left foot, then I've matched the movement of my upper body with my lower body and transferred the maximum amount of energy to the ball. It's also a sign that I've correctly shifted my weight to my left big toe.
The old "swing in a barrel" theory has merit. Never feel like you're sliding or swaying in your swing. If you sync your upper and lower body and shift your weight correctly, you'll feel like your hips are turning directly over your feet.