Cutting hair is an art form and there's really not a right or wrong way to achieve great results with a haircut. Each approach will vary by stylist, but there are some basic principals that all barbers and stylists can implement to improve speed and quality when cutting men's hair. Good technical skill will also help increase your male client retention.
Wet or Dry?
Clipper work is almost always performed best in dry hair. It is my opinion that blending should also be done in dry hair. When the hair is wet, it can be difficult to see lines and hard to tell exactly how the hair is going to lay when cut. The hair should be wet for most shear and razor work.
When performing a haircut, cross-checking is essential. To some, this may seem like an unnecessary step, but it is important to make sure the cut is even and proportional. When doing a short haircut, check for blending and tapering in the mirror (or stand back a few feet). Often, you can see things from a distance that you will miss up close. Also, make sure to have proper lighting from all angles. Dim light and shadows make it very hard to check for quality in the cut.
The first step in good blending is avoiding lines of demarcation in the first place. When performing clipper work, go through three steps with each stroke. Start with the clipper anchored with the entire flat surface of the blade touching the head. Moving upward, pivot the clipper so only the heel (back) of the blade is touching. Next, suspend the clipper freehand as it moves up and out of the hair. This will create the smoothest transition possible.
One method of blending between clipper and shear work is to use the clipper-over-comb method. For this technique, use a detachable blade clipper with a large blade (#1 1/2 or higher). The larger blade will give the client a smoother blend because the hair will be cut a uniform length with a feathered end. Never use a short blade or trimmer to blend because the blades will give the hair a very blunt cut and leave lots of small lines of demarcation.
Blending: Blending Shears
Another method of blending is blending-shears-over-comb. Lift the hair up with the comb and use the blending shears to cut the last 1/4" of the hair. When lifting the hair, it is important to slightly overdirect before cutting as this will produce a smoother blend. Remember to only cut the last 1/4'" to 1/8" of hair. Never thin hair close to the scalp as this will create a fuzzy look by causing very short hairs to stick out through the longer hairs. Use a thinning shear with at least 40 teeth. Shears with larger teeth will produce lines. Avoid using regular shears to blend because the blades will give the hair a very blunt cut and leave lots of small lines of demarcation.
Blending: Haircutting Razor
You can also create a blend using a standard straight razor (without a comb attachment). The hair is raked with the razor at a 45-degree angle. The angle of the blade is very important. If the blade is held in a more flattened position, too much hair will be removed. If the blade is held more upright, it will damage the cuticle. This technique was made popular by the Roffler schools and should not be attempted until you have received hands-on training by a barber/stylist who is skilled in the technique. For razor blending, it is essential that the hair be very wet.
A razor (with guard) or shear-point techniques can be used to give the haircut texture by cutting the ends of the hair in obvious, varying lengths. Texture is desirable in haircuts that are worn spiked or disheveled. The razor (with guard) is used to strip the ends of the hair between the blade and the thumb to create the varying lengths. When pulling the hair between the razor and thumb, hold the razor at an angle and use a scooping motion. The shear-point technique is used to cut the ends of the hair at an angle (or even snipping out alternating pieces) to add texture. Perform these techniques only after hands-on instruction from a qualified instructor.
Many stylists will spend a great deal of time making sure a haircut is well blended and even, but skimp on the finishing. A great haircut can be completely destroyed by poor finishing (a bad haircut can also be made respectable with good finishing). It is critical to make sure all lines (the arch around the ear and the neckline) are clean and neat. Most haircuts will also benefit from slight tapering or beveling around the bottom edges. When doing sideburns, stand in front of the client and look him directly in the face to ensure evenness. Check to make sure bangs are straight as well.
Necklines: Blocked or Tapered?
Many stylists and barbers will take the shortcut of blocking the client's hairline. Often, this can be a disservice to the client. A tapered haircut will give a wide neck a slimmer appearance and will look neater as the cut grows out. On a blocked haircut, the neck hair will grow out below the block and the client will have a line in the hair on the back of his head. A tapered haircut blends with the hair as it grows out. Blocking can give a slim neck more balance, so it is often a good option. When blocking, the hair should be blocked as low on the neck as possible so there will be less hair below the line as the cut grows out.
Many in the industry are firmly against the use of clipper guards. The main argument against guards is that anyone can snap on a guard and give a haircut, so the feeling is that many clients will attempt to cut their own hair. The fact is, however, that most clients will not be able to get professional looking results at home. Only those trained in cutting hair will be able to accomplish the proper finishing, blending, and tapering needed to make a clipper cut look professional.
As for technique, there are a few things to keep in mind if you choose to use guards. When using a clipper with guards, follow the anchor-pivot-suspend technique and cut against the growth pattern. Avoid cutting at an angle as this will create small lines because of the way the guard separates the hair before it feeds into the blades. Next, make sure to go over each section of the hair a few times to ensure all hair is cut. Avoid forcing the hair into the cutting blades with a comb or your hands as this will create lines of demarcation. Always comb the hair before each stroke, but make sure the comb is out of the way before the clipper runs through it. Finally, avoid guards that leave the hair longer than 1/2 inch. Clippers will only effectively cut hair when there is enough tension on the hair to force it into the cutting blades. Larger guards do not allow enough tension and, thus, will leave much of the hair uncut.
Above are but a few of my thoughts on appropriate techniques for cutting men's hair. Again, there is no right or wrong way to approach a haircut as long as the end result is technically solid and the client is thrilled.