Take It Away
Like the setup, a proper takeaway is absolutely critical to making solid swings that produce consistently good contact. The mistake I'm making here (to the left) is taking the club too far to the inside, which typically leads to a steep move at the top and an over-the-top downswing. To fix this, place a water bottle directly behind the ball at address and try to take the clubhead straight over it as you make your move away from the ball. When you get the club moving in the right direction at the start of the swing, it's much easier to keep it on plane on a consistent basis. Try this drill, and you'll soon see what I mean.
A proper takeaway has the clubhead moving straight down the target line. Don't let it get too far inside at the outset.