Prop the phone up and arm the camera. It waits for you to settle over the ball,
starts on its own when you take the club back, and stops after the finish.
Phone at hip height, 7–8 feet away, propped against a bag works fine
Down the line means directly behind you on the target line — that's the view that shows a slice
Whole body and the full club arc in frame
Keep people and carts out of the background so nothing else trips it
Start here
What's costing you
Work on it
The overlay lines are an estimate drawn from the still images, not motion capture.
Treat them as a coach pointing at a screen, not as measured numbers.