When you are going to sleep at night, take out any clips or bands that you have in your hair. When your hair is pulled back in your sleep and you move around, you could cause your hair to break off. Also, use a satin pillowcase, if possible, so that your hair glides when sleeping.
When you see gray hair start to appear on your head, you should not pluck them. Most people believe that it's because two will grow back in its place, but the real reason is because you can damage the root of your hair by pulling it out. That could lead to an infection at some point.
Do not put too much stress on your hair, if you are going to pull your hair up into a pony tail or braid it you should do it gently and not pull it too tightly. Also if you are going to brush it do it gently and softly.