If a man has short hair, he might be more likely to entrust it to a friend when it needs a quick trim. In the skilled hands of a professional hairdresser, clippers are just another useful tool, but in the untrained hands of a friend, he could end up with a stripe of bald head when the helpful buddy accidentally uses the attachment with the zero setting. And curly hair is more complicated to cut than straight hair. Despite the chance of a mishap, a home clipping does save on the price of a professional cut.
Ensure the hair is dry. Wet hair gets caught in the clipper blade, and the water can rust the metal. Curly hair is also sometimes longer when it is wet than when it is dry. If you choose the cut length when it is straighter, you could misjudge the desired length. Freshly washed curly hair is also less suitable for clipping than hair that has settled into its natural, clean but not freshly washed, style.
Fit an attachment that is long enough for the desired finished cut. The longest common attachment size is about 25mm (about an inch) and is called a number eight. The lesser valued attachments get shorter as the numbers reduce, until they get to the blade without an attachment which is called a zero and cuts very close to the scalp. If you are unsure which attachment is the right length, start off with the longest one as you can always switch to a tighter attachment.
Pick up a small section of curl at the back of the head. Place the clipper blade with attachment under this section and run the clipper upward against the direction of the hair growth. If the clipper does not slide through easily, or if the blade gets clogged, restrict the amount of hair to about half the width of the clipper blade and continue cutting.
Clip another section of hair with the clippers in the same manner and repeat this technique over all the sections of hair you wish to cut to that length. If the man wants to keep some length, an all-over cut of the longest attachment will leave him enough to style with gel if he wants.
Swap the attachments over if you want to give different parts of the hair different lengths. For example, if the man whose hair you're cutting wants to lose his curls altogether, you can cut all over with very short attachments or even down to a zero, which will give him a skinhead style. A garden-variety short back-and-sides requires longer hair on top and a shorter cut on the sides and the back.
You can use clippers on longer curly hair if the man doesn't want to go as short as the attachments allow. Simply use the clipper to trim the tips of the dry curls off with temporary swoops rather than keeping the clippers in permanent contact.