As a grad from one of the nerdiest schools you're going to find, I end up meeting a lot of people with long hair. For women, this isn't such a weird thing, but we have a fairly significant quantity of males with long hair of various magnitudes. As such, I wrote a primer on how to deal with long hair.
This isn't to say that all guys don't take care of their hair, by any means, or that all girls do. In the end, there are many on both sides who just sort of ignore it. Without further ado, some helpful tips from someone who has had long hair for 20 years. Note that I have straight hair and, as such, can't give as helpful advice for very curly hair. Wavy hair acts similarly to straight hair in a lot of ways, from what I've seen, but grain of salt and so forth.
1. Cut your hair.
I know this is counter-intuitive. You want to grow your hair out, so you ignore it and let it grow, right? This is incorrect, especially if you have blonde hair. Dark hair is thicker per strand than light hair, on average, so it tends to suffer less damage per unit time, but in the end, all hair will have split ends. Split ends are when the hair shaft divides near the end of the hair, causing a frizzy clump of skinny hair tips that gives your hair a ratty, tangled look. They make the hair weaker, and the longer they're around, the higher up the hair will split. Eventually, you can get inches of split ends, and it's made even worse if your hair deals with chlorine, heavy heat, salt water, or other such abuse on a routine basis. A friend of mine went hiking in the desert for three months and had to get about four inches of hair chopped off because it was utterly destroyed.
The solution to split ends is to trim your hair about half an inch when you see the frizz starting to appear. Don't cut it often, or much -- just go to a stylist or a friend and tell them to take the split ends off. Your hair grows faster than its ends split, so you'll slowly grow your hair out and keep it nice-looking. There's little sadder that can happen to hair, than having a foot and a half of ponytail with the last six to eight inches being ratty split ends.
2.Get a separate conditioner from your shampoo and use it every time you wash.
Conditioner is in no way overrated. When you shampoo your hair and nothing else, you strip off all the oils but put nothing back on to protect the hair. As a result, your hair gets dry, damaged, and brittle. When you brush it, it will break. Those two-in-one shampoos are atrocious -- shampoo strips off oil, and conditioner tries to moisten, and the two do not work well together. First shampoo, then condition. If you have particularly damaged/brittle/dry hair, leave the conditioner on for a few minutes, and consider buying something you can leave in after you wash.
When you wash with conditioner, make sure that you're not over-rinsing it. Notice how, after you shampoo, your hair gets that "squeaky clean" feeling where your fingers cause enough friction to actually catch on the hair. After you condition, you should stop rinsing when your hair feels smooth but not slick -- your fingers shouldn't grab in the hair, but nor should you be able to feel the conditioner either. It's a practice thing, but in the end, that's the magic point where the conditioner is doing its job without leaving a residue.
3. Don't use crap conditioner.
I know it's tempting to buy a two-dollar bottle of conditioner, but up to a point, you really get what you pay for. Six to eight dollars is the minimum for good conditioner on my hair; it probably varies per person, but if you're using a cheap bottle of Pert, it simply won't do much for you. It'll be like you didn't condition, and see above for the consequences.
4. Use a brush.
I know this sounds ridiculous. Still, some people don't brush their hair. Granted, some people's hair is magical and doesn't tangle, but that doesn't mean you shouldn't brush it. Brushing hair flattens the flyaways that form halos around your head after you wash, and it gets rid of shed hairs that are caught up in the rest of your hair. Finger-combing isn't going to get all of them. Even if you're losing hair, brushing softly isn't going to tear out any more; it's just going to remove the hair you've already shed.
There are two different kinds of brushes, loosely: bristle brushes and rubber-nib brushes. Rubber-nib brushes are the most common kind; they have spines that have rubber bulbs on the end. They tend to be stiffer and dig farther into the hair, which means that for most people they're better at getting all the tangles out, but for people with sensitive scalps, they're little torture devices. If you're like me, and pulling at your hair causes you nontrivial pain, you should use a bristle brush, which has thinner and more flexible strands with nothing on their ends. Bristle brushes are less powerful than rubber-nib brushes, but they're gentler. Try each one and see what you think. Most people prefer the nibs, but a few just can't deal.
Brush your hair from the ends upward. This will brush out any tangles without clumping them together at the end of your hair. It can be slow going, but it will do less damage to your hair in the process and make the tangles easier to get out.
5. Tame flyaways.
Fine hair tends to be really fluttery. Chances are that if you have fine hair, you get shorter strands flipping about and giving you a vague halo a la those Catholic saint pictures. What you can do for this is to take some anti-frizz cream or some hair shine liquid and rub a tiny bit on your hands, then run your hands through your hair. That should be enough to keep the loose strands back.
6. Pull back your hair.
I know ponytails aren't for everyone, but find some way to tame your hair when you need to. It will get in your way during sports, on windy days, and so on, no matter how much you like to wear it down. Sometimes it's just worth it to carry a hair tie or two. Get the kind with no metal -- the metal bits on old hair ties will snag strands and hurt when you pull them out of your hair. And seriously, don't even consider using rubber bands.
7. You don't need to go to a stylist to cut your hair.
Friends can trim long hair as long as you don't have a crazy cut. If you've just got hair of a fairly uniform length, all said friend needs to do is flatten your hair when it's wet and trim straight across. Put it in whatever part you like (middle, side, whatever) before the cut is done. If you have wavy hair, this gets even easier, because it's harder to see a slightly uneven cut on curly or wavy hair than on straight hair. Granted, if you want a special cut, you will have to go to a salon unless you know a particularly skilled friend, but odds are if you're an average guy with long hair, just get a friend to snip the ends off once in a while. It takes ten minutes, tops.
8. Consider a hair dryer if you have to look particularly nice.
I know hair dryers are said to completely ruin hair, but this is utterly false. They do some amount of damage, but it's nothing conditioner doesn't fix. As long as you don't over-bake your hair, you'll be fine. Hair dryers prevent hair from looking oily after you wash. When you dry your hair, keep the dryer moving so that no one section of hair sustains too much heat. Take a brush and brush your hair while facing the dryer toward the bristles; this will help it dry faster and look smoother. If you're one of those people that likes curling the ends, you can get a round brush and make some waves at the end of your hair by wrapping your hair around the brush and drying as you pull the brush through.
9. If you have oily hair, only condition the hair that is farther from your scalp.
Don't put conditioner directly near your scalp if your hair gets oily. Your head will naturally condition the roots of your hair, so worry about keeping the length from being damaged and breaking off. Conditioner will only force you to wash your hair more often to keep the greasy look away.
10. Try not to brush your hair harshly while it's wet.
Brushing wet hair tends to break it, so be careful. Combing is better, but long hair tends to resist combs.