To promote clubface rotation make sure your left hand grip is turned back enough and then take half swing concentrating on the rotation of your forearms
Although his swing looks a little loopy Jim Furyk is a great example of a one plane swing, he takes the club outside coming back but his delivery position is exactly on one plane.
Working on a computer or gripping a steering wheel can cause your wrist extensors and flexors to stiffen up and limit their extension in your golf swing