Up And Down Vs. Around
It's easy for a player trying to break 100 to get overwhelmed by a lot of technical instruction. A lesson where you're bombarded by mechanical thoughts is a failure, because you can't incorporate so many things into your game at once. We always start our lessons with simple images, like the Ferris wheel and merry-go-round below. Getting a picture in your mind of swinging up and down or more around your body is a much easier and more productive starting point for understanding a swing than specific technical advice about things such as plane and path.
On shorter shots, it's tempting to freeze your body and try to make a smaller, arms-only swing. Even though you're hitting a shot 40 or 50 yards, you still should get your whole body involved in the swing. A simple way to visualize a good lower-body motion is to imagine a party hat connected by elastic to your right knee (right). The tip of that hat should point at your target when you finish your pitch swing.