The clipper-over-comb cutting technique is good for sides/sideburns and the bottom area of the haircut by the neck. Some general guidelines to follow are:
* The hair must be dry because wet hair clumps and therefore won't get cut evenly by the clipper blades. Do the clipper-over-comb technique at the end of the haircut. When you start cutting at the beginning of the haircut, the hair needs to be damp. However by the time you've finished the outline and the top ½ of the head, the bottom should be dry enough to cut with the clippers.
* Hold your comb in your less dominant hand (left) and lift vertical sections of hair at a 90° angle (straight out) from the scalp.
* With your clipper in your dominant hand (right), start at the bottom of the section of hair protruding between the teeth of your comb. Move your clipper up your comb, cutting off any hairs that stick past your comb.
* If you want to taper the hair with the bottom being the shortest and having the top of the section you are cutting to be longer, you'll need to angle your comb. When you lift out vertical sections of hair, have one end of the comb close to the head and angle the other end out. Hold it at the angle that makes most sense for the haircut you're giving.
* Keep cutting in vertical sections around the head. Work from the bottom of the hairline, going up until you reach the bottom of the hair that is already cut at the top of your head.
* With this technique, your comb has the most important role because it determines how much hair you are going to cut off. Hold the comb steady as you are cutting to avoid any unevenness.
* Use hair that you've already cut to act as a guide for how you hold your comb. Picking up some hair that's already been cut along with some uncut hair helps you to see how to hold your comb for the next cut. Be careful with the first cut you make since you have no guide for it. Be conservative with how much you cut off the first cut. You can always go back and cut off more if needed.
Using the clipper-over-comb cutting technique is a real lifesaver for hard to cut areas at the bottom of the haircut. You can make the bottom edges much shorter (and therefore make the haircut last longer) if you pick hair up with a comb rather than with your fingers.