Swing two clubs parallel to each other back and forth trying to keep the clubs from clanging together, this works your timing as well as coordinates your body with your arms
An inside out swing approaches the ball on the downswing from too low, hitting the half of the ball closer to the player, causing a push or hook which requires the player to work on getting the club further up and out on the downswing
Use a piece of string to fix your swing path by placing a ball inside or outside of the string, when you come down to hit the ball you can get a perfect visual to see if your club is traveling inside out or outside in