Even with the best fundamentals, it's too easy to get quick with the start of the downswing when we are trying to hit it extra hard or because we're a bit nervy. This usually leads to the clubhead casting or the body lunging forward on the downswing, resulting in a loss of distance and direction -- commonly referred to as "coming over the top."
Swing thought: Completing a full shoulder turn, keep your back to the target as long as possible during your downswing. Feel your arms leading the swing as they fall at a speed close to a gravity drop. Soon you will begin to feel your downswing path coming much more from the inside with a shallow angle of approach into the ball.
Drills: Tee to ball. Place a tee into the grip end of your club. Begin the downswing by pointing the tee at the ball. This will help establish a proper downswing path.
Gravity drop: Extend your arms out at shoulder height. Let them fall by force of gravity down to your sides. Take that same feel to the start of your downswing.