There are several ways to draw out a template showing the position of the mirror and incident ray with respect to the normal.

Below is the one the Figure Out Physics staff use:

This is vital as without it you cannot verify the law of reflection accurately. To be able to accurately measure the reflected and incident angles, you need to know their position with respect to the normal, and to know where the normal is, you need to accurately mark there the mirror is. To achieve this, you must draw out a diagram similar to the one above.

The next learning objective shows how to line the mirror up with the line.