One of the biggest imperfections in amateurs' swings is not swinging the club on plane. To swing on plane, your club needs to go around your body parallel to the original shaft angle at address. Swing planes can vary, and it's all based on your posture--how vertical you are--when you step up to the ball. While never easy, working on developing swing plane will help you generate consistency in your swing and straighter shots.
Step up to address.
Sole the club on the ground. This means that your club bottom, or sole, needs to be flat on the ground, not raised up on either the toe or the heel.
Check your shaft alignment. The club shaft should run up from the ground so that it points at your midriff, or along the belt line.
Get your body over the ball. The basic idea is that your hands should be able to comfortably grip the club without having to extend your arms. From your shoulders, your arms should drop straight down.
Draw the club back in a slow motion swing, constantly checking to make sure that your shaft angle is staying consistent with the original address angle. .
Continue through impact and follow through keeping an eye on what your shaft angle is doing.
Make yourself comfortable with the swing motion by practice the swing at full speed.