Using a comb as a haircutting guide is another technique you can use when cutting your own hair or someone else's. It is similar to the clipper-over-fingers technique, except you use a comb instead of your fingers to cut hair to your desired length.
Steps for Using a Comb as a Haircutting Guide
With the bristles of the comb up, comb the hair upward from the back or toward you from the front, and stop before the hair leaves the comb.
Run the clipper across the comb to cut the hair to the desired length.