Swaying in your swing will cause miss-hits the online golf coach recommends this drill.

Place a shaft in the ground by your left hip/foot can create a visual aid that will help to stop your sway.

This will certainly stop you swaying on the downswing and will also promote the feeling of turning on the way through.

All you need to do is make your normal swing focusing on rotating inside the shaft rather than too much lateral sway.

You can also place a shaft outside the right side to help prevent any sway in the backswing.