In a nutshell, the process involves trimming all your hair to one length, and then cutting down the sides and back further to get a tapered, neat appearance.
However, cutting hair by yourself is still a somewhat tricky procedure. If you haven't done it before, it could very well lead to disaster, so don't do this the day before your big job interview. That said, it gets much easier with repeated practice. It'll probably take 20-30 minutes to cut your hair, especially if you've never used clippers before. So take your time, you'd spend even more time at the barber's, and, if you like to maintain a clean-cut appearance, the $10 you spend on clippers will pay for itself dozens of times over.
Besides, hair grows. Right?
Step 1: Supplies
These are going to be the most important part of your operation. Pictured are a set of Wahl clippers, which are popular since they're usually the cheapest out there. If you buy clippers, make sure they come with a good assortment of blade guards.
Second most important. Usually they come numbered, although many will also be color-coded and/or have actual length measurements on them. If not, as I understand, the numbers are increments of 1/8", so a #8 blade guard will be an inch.
You're going to use this to look at parts of your head other than the front, in tandem with the big mirror. I stepped on mine this afternoon, cracking it. Yours should not be cracked; it makes this really hard (and kinda dangerous!)
This, with the hand mirror, will give you just about all the views you'll need of your head. Make sure this one is big, and mounted to the wall, since you can't hold two mirrors and a set of clippers.
This is where you're going to put the hair you cut. You're going to want it right there, if possible, so you can just cut your hair and let it fall straight in there.
This is a good thing to have, too, since otherwise you'll have to sweep up frustratingly small bits of hair off your floor. This is just a shopping bag cut open.
Step 2: Preparation
Also, realize that while 8 seems like a big number, an inch of hair isn't all that much. While the blade guard will give you an idea of how long your hair will get cut, when it's on your head, your hair will lie flat, making the actual length surprisingly shorter. In this Instructable, I'm cutting with a #6 (3/4") on the top and a #4 (1/2") on the sides, so you can get an idea of what that looks like here. I tend to think 4 and shorter is super-short.
You'll want your hair to be dry, and relatively clean. A little bit of styling gel from earlier in the day won't matter, but you'll want your hair to be loose all over so the clippers can push all your hair freely and cut it all to the same lengths.
Also, I'm going to recommend that you take your shirt off for this. That's totally optional, of course, but the hair you cut tends to lodge into the weave of fabrics, making it super itchy and sometimes taking repeated washes to get out. So taking your shirt off just saves you some hassle.
Step 3: The First Cut
When I cut, I usually hold the clippers like I would a pencil. Well, a large, electric pencil. This allows for a fairly natural control of angle and turn as you move the clippers over your head. However, depending on the angle, you'll want to change your grip to whatever feels natural and allows you to move the clippers in a way you can mentally visualize easily. Mental visualization becomes important in the next step.
Now turn the clippers on and run them through your hair. In this step, you'll probably cut the most hair, so you'll want to hold your head over the trash can so most of the hair falls straight in.
When cutting your hair, you want to go against the natural grain of your hair so the guard can straighten the hair to vertical so the blade can cut it at the correct height. This generally means from the edges of your hair to the little whorl of hair in the back of your head. You should be able to hear the gzzzzzt sound of hair being cut over the sound of the clippers. Take the clippers all over your head, making multiple passes over every area. You don't have to cut absolutely every hair, but the goal is to be thorough, since you don't want one little patch on your head to have an awkward peak where you missed a spot. Spend particularly close attention to cutting the hair around the whorl in the back, since hair there falls at odd angles and tends to lie flatter than in other parts, so it's easy to miss substantial amounts of hair back there.
Step 4: The Sides
Of course, you probably didn't need an Instructable to tell you how to do that. Now comes the tricky part - the fade. A good looking haircut probably means your hair is longer on the top than on the sides. So snap on the guard you want for the sides.
I usually pick a guard 2 or 3 lower than the original cut, so here I'm using a #4. However, if you want a bunch of hair on top with short sides, I'd recommend doing this step in parts, again cutting with the longer guard first then the shorter one.
Basically, you're going to cut the hair on sides of your head short, but blend it into the longer hair on top. There are basically two ways to do this, and you'll most certainly use both to some degree. Remember, though, the clippers cut hair at the back end of the guard, so you'll need to take that into account when thinking about where the clippers are and where they've cut.
Take the clippers and run them horizontally from the front of your head to the rear, holding the bottom edge of the guard against your head and the top edge in the air (Picture 1).
Method 2: Run the clippers up from the bottom of your hair and then run them straight into the air along an imaginary line where you want the transition of short to long hair to be. With this, make sure to keep moving into the air, since otherwise you might not cut the entire line, leaving a little ledge of hair. Also, when moving, you can tip the tips of the guard into your scalp, putting more room between the blades and your hair.
Cut the hair on both sides of your head, then go to the next step.
Step 5: The Back
This is where the hand mirror comes in. Holding the hand mirror in your non-cutting hand, angle it towards the big mirror so you can now see the side of your head in the hand mirror. This will let you see the profile of your hair from almost any angle, and that profile will be what you use to judge most of your cutting from now on.
Starting from the side, continue the same general slope of cutting around the back of your head by looking through the mirrors. Go slowly; you're now looking through 2 mirrors, so the motions of your hand and the clippers are now reversed, making fine movements difficult.
Again, the whorl will give you a host of problems if you're cutting up in that area. A good rule of thumb is, 'if it ain't broke it, don't fix it'.
Oh, and don't use a broken mirror like I did. It's really, really hard to see the profile of your hair when it's all jagged.
Step 6: Final Touches
If you want to cut a clean line at the base of your hair on the back of your neck, use either the #1 guard or none at all and, looking in the mirror, flip the clippers upside own and cut in downward motions from the line you just cut.
Step 7: Clean Up, Take a Shower
Once your workspace is fairly clean, go take a shower; otherwise, you'll be leaving little hairs all over. However, when you shower, before you get your hair wet, apply a generous amount of shampoo. This way, the shampoo will bond directly with the bits of cut hair, meaning you'll get most of it off your body in the first rinse. Still, you'll want to shampoo your hair multiple times, until you can run your hand through and it come out with only a few hairs.
Once you've dried off, admire your new haircut! You might notice a couple of little places you missed still, but those should be pretty easy to fix. If, on the other hand, you're not really satisfied with it, I'd recommend to wait a couple days; it usually takes a little bit to get used to a new haircut, so odds are going back and cutting it more won't improve things.
Now go out, get some clippers, and rock a new haircut!