Use visualization to cure an outside-in swing. Address the golf ball, raise your club about a foot or two above the ball and then make your backswing. Take note of the plane of your backswing and take your downswing inside of that plane.
Ask a fellow golfer to take a video of your swing from both a side and back view. Once you understand what it takes to hit the ball correctly, you can look at the video and see where you are making mistakes.
Your goal is to develop a simple swing that you can easily repeat.