There are a couple of good full swing drills that I like which help well with full swing alignment.
One, you can always lie down an iron on the ground (pointing at your target) when you’re hitting balls on the range. Then line up your feet, knees, hips and shoulders on that same line to get a feel for how to aim.
But an even better technique is to do what Nicklaus did. Pick a spot (a patch of grass, an old divot, an old cigarette or just whatever) directly in front of you, in the same line as your target, and line up to that spot, as targets are so far away that it’s oftentimes very easy to misalign yourself.