This is quite long so I apologise, scan through to find what parts relate to you and your hair.
I try to keep my hair as healthy as possible because I have seen how horrible damaged hair can look.
Here is how I keep it healthy:
Basically... Do Nothing
Now, this may sound silly. How can I get my hair to be healthy without helping it?
Using Heat:
But the only thing that ruins hair is doing too much stuff to it. Such as using heat on it.
Don't get me wrong, I love my hair after it has been blow dried and I curl and straighten my hair. Just not every day.
Let your hair dry naturally unless you have something you need to go to and don't want wet hair. But even then, try not to blow dry it totally bone dry. Stop the hair dryer when it is still ever so slightly damp. This way it won't dry it out as much.
Also, use a tiny bit of heat protectant on your hair before. Only a little bit as it may make it a bit greasy if you use too much.
Hate your natural hair?
If you hate you natural hair, don't use heat on it every day. This frazzles the hair so much and it is very hard to get it back to what it was.
If you have straight hair like me, put it in dutch or french braids before you go to bed to create beautiful waves in the morning. And when this is the case, don't use too much hair spray on it to keep it wavy.
Some peoples hair hold curls better than others. Mine is useless when it comes to curling and falls out within hours. However, I know people that can curl their hair before bed and it is still in perfect curls two days later.
Naturally curly hair can be hard to manage as it gets knotted very easily. This is why when you got to bed brush it before and then put it in plaits.
This isn't to make it wavy like for people with straight hair but to keep it tight and together so it can't spring out and tangle. This will make it much easier to brush in the morning.
If you want a way to sort out the curls you can straighten them. But this is going to dry out your hair and I think all curls are beautiful. I would do anything to have curly hair as it does look nice even when you haven't done anything to it.
Look for an anti-frizz spray in your local Boots or any hair shop. This will define the curls and stop them frizzing.
Instead of straightening with straighteners, after washing your hair blow dry it straight with a brush. I find this holds better than straighteners so you don't have to do it as often.
Washing your hair
DO NOT WASH YOUR HAIR EVERY DAY. You need the natural oils in your hair to keep it healthy. This doesn't mean you have to let it get greasy, just let it have a day of rest in between washing.
I would advise you not to wash your hair every other day either. This is better then everyday but it still takes any natural goodness our of hair before it can use it properly.
I know that every one has different hair types and that some gets greasier quicker than others but that is partially down to routine.
If you wash your hair every day it will get greasy in a very short time. The hair will be rushing to get natural oils on it to moisturize it and make it healthy.
Washing you hair twice a week or once is best. Obviously if you do a lot of work and get your hair sweaty then it is better to wash it.
Dry shampoo is great if your hair does get greasy quickly because it doesn't wash the goodness out, just absorbs the oil to make it less noticeable.
I suggest Batiste dry hair shampoo. It is the best I have used and smells amazing.
I am not a professional in all of this but I have taken this information from experience and observation.