Determine a line on the paper to place the mirror on, mark this line and mark the mid-point.
Draw a line from the midpoint perpendicular to the base line - this is your normal and all angles should be measured from this line.
Shine the laser so that it hits the mirror at the midpoint - mark two dots in the centre of the laser beam incident to the mirror and two more on the reflected ray.
Use the ruler to mark in the path of light and measure the angles of each beam from the normal.
Repeat this process another 5 times for different angles of incidence.
You should find the angles on incidence and reflection are the same, however there may be some variance. Sources of error include how well the points in the rays were marked, how well the lines were then drawn with the ruler and finally your proficiency in using a protractor.