Sectioning the hair

Divide the hair into four sections.

Make a part from the front center hair line back to the crown.
Start at the center of the part and draw a straight vertical line down to the back of the ear.
Clip the front part out of the way and repeat on the other side.
You will now have 3 sections.
Now extend the center line down the back of the head to the nape.
Clip one section out of the way and you can begin the hair cut on the side that is left down.

More on How to Cut Hair.