One thing I learned early in my teaching profession was to take tilters which is the majority of golfers who are struggling and learn how to make them turners.
If you slice the the ball and/or end up on your back foot and never seem to be able to get onto your front foot at finish most likely you are tilting during your backswing. By tilting what I mean is that your front shoulder (left if you are right handed) goes down towards the ball. What is happening is that your shoulders are working in too much of an up and down movement rather than staying level and turning across and behind the ball.
The fix: Try and turn your shoulders more level and make your left shoulder feel as if it is turning straight across your body to a position that is even with or behind the ball. Try this backswing tip out and see if it doesen’t help you make better backswings and hit better shots!!