I'll show you my method for cutting my own hair using scissors and some clippers for detail work. Save money and time!
Step 1: You Will Need...
a good pair of ambidextrous scissors (that can be used in either hand),
a small mirror,
an electric clipper,
one or two plastic garbage bags to catch the messy hair clippings, one for the counter, and one for the floor.
These should all cost you less than $30 U.S. ($10 Canadien), but these will pay for themselves after one or two haircuts, so go ahead and get a very good pair of barber's scissors.
Step 2: Wash Your Hair, Then Cut the Hair in Front
Wash your hair and towel it dry.
Then, comb your hair, and get the part in exactly the place that you want it.
Next, comb your hair so that it's hanging down over your forehead and eyes.
Finally, cut the hair over your forhead so that it's just above your eyebrows. If you cut the hair much shorter than this, it will stick up and be unmanageable when it gets dry.
Step 3: Cut the Hair on One Side of Your Head.
Then, tilt your head so that the side with the part is facing up, and the hair on the opposite side from the part is hanging down.
With your fingers, pull the hair down so that it is hanging straight down.
The hair in front should be hanging down to about where the yellow line is in the first photo. What you want to do now is cut all the hair on the side of your head to that length, a bit longer near the top of your head, and rather short near your ears. The angle of the yellow line in the picture shows the length of the side hair that I am trying to get.
Use your scissors to cut all the hair hanging down on the side, until its length is about even with that line.
As you cut further towards the back of your head, try to follow the curve of your skull, so the hair is the same length all the way around toward the back of your head. Just do this as far as you can see it in the mirror - don't try to cut it like that all the way around the back, just as far as you can see in the mirror.
Step 4: Now for the Other Side.
Use your fingers to pull it all straight down.
Now, cut the hair on this side of your head so that the length of hair on this side matches that of the other side. Again, the yellow line in the photo shows the length you should go for, slightly longer at the top of the head, getting shorter near the ears.
I am right-handed, and I have my part on the left side (these pictures are taken in a mirror, so they are reversed). This means that for this side of my head, I have to use my left hand to cut. My scissors are made for this, but it takes a bit of practice before you get any good at cutting your hair with either hand. Just watch what you are doing, go slowly and carefully, and you should be fine.
Once again, try to cut the hair so it's the same length around the head toward the back, but only go as far as you can see. Cutting the hair in back is done using a different technique, and we'll deal with the back of the head momentarily.
Step 5: Cut the Hair on Top of Your Head Next.
Well, we already cut the hair at the very front, over the forhead, and that's the length we want, so now we just need to cut the rest of the hair on top until it's the same length as the hair in front.
To do that, make a comb with your fingers and run it through your hair on top of your head, near the forehead. Pull your fingers away from your head until you see the hair at the very front is just sticking through your fingers. This means that all the hair that's still sticking up through your hand is longer than the forhead hair we cut earlier. In the photo, that's shown by the orange line.
Now that you have the length, and all the hair above the hand (sticking up between your fingers) is too long, take your scissors in the other hand and lay the scissors on top of the hand holding the clumps of hair, and cut off all the hair above the hand, so that the remaining hair (under your hand) is the same length as the hair over your forehead. Be careful not to cut your fingers!
You may notice that, at this point, you're cutting your hair more by feel than visually. You get the length of the hair visually, but laying the scissors on your hand and cutting the hair doesn't require your vision, just your sense of touch. This is how we cut the hair at the back of the head - use your hand as a comb, feel for the length, and the cut all hair beyond that length. You can't cut it too short, and you can do everything by feel.
Anyway, let's not worry about the back of the head for now. We have to finish the top of the head first. Once you have that first handful of hair cut down to size, use the finger-comb method on the hair that's a bit further toward the back of your head, to about the same heaght, using the hair you cut in the last handful to guide you on the length this time. You can make the length of the top-hair a little shorter as you go further back, by making the hand holding the hair go closer to your head, but don't get too much shorter than that, or the hair in the back will stick up like Alfalfa (or Dennis the Menace), and you don't need a rooster tail back there! Anyway, keep working your way toward the back of the head, finger-combing and cutting.
The further back you go, the more you will be cutting by feel. That's the way it's done.
Step 6: And NOW: the BACK of the Head!
Once you've cut the hair at the very back, cut the hair on the back left and back right of the head, working your way from the top of your head down to the collar. Usually, I have pretty much already cut this area, when I tilted my head and cut the hair on the sides, but it's good to make sure that the hair all around the back of the head is cut.
Step 7: The Finishing Touches.
As long as you have the clippers out there, trim the beard and 'stache.
Finally, turn so that your back is facing the mirror. Hold the small mirror in one hand to see the back of your head in the other mirror, and use the electric clippers in the other hand to trim the hair above the neck to a nice even line. If need be, shave off the hair at the back of the neck, too. You can kinda do this by feel, but I'd rather use the small mirror to see what I'm doing.
That's all the cutting you need to do! Just pick up the hair clippings by rolling it up into the garbage bags, and hop in the shower to wash the hair clippings off of your body.
Step 8: The Result!
The back of the head isn't perfect, and if I were going on an interview or something, I would have my hair cut by a pro, but this is good enough for work situations, or class, or just everyday hanging around. Not too many people will judge you by how perfect the back of your head looks (if they do, maybe they need to lighten up), so don't get too hung up about the back of your head.
The main thing is, this actually doesn't take very long to do, and it's WAY more convenient than going to a barber, waiting for a barber to get to you, and then getting a look that isn't quite right the next day. This way, you have the power to correct a few stray hairs after the fact. As with anything, the more you practice with this, the better you will get, and in the words of America's foremost hair stylist, William Dauterive, "it WILL grow back." Persevere!