When you are sad, you need to find ways to deal with your sadness. When you learn how to deal with your sadness, you'll find your own happiness.
Accept your sadness. It's not a bad thing to feel sad. Try to face what is making you feel sad. Don't pretend it isn't there. And don't believe it will just go away by itself.
Speak about your sadness. You don't have to tell everybody everything, but it is nice to talk to friends or family about your feelings. You may not need him or her to say a word; just having someone to listen to you is sometimes enough.
Put your sadness into written words. Write down how you are feeling every day and why you think you are feeling this way. Write down how you deal with your sadness and which ways work.
Take part in activities. Read a good book, listen to music, exercise or take a walk outside. These can help you feel comfortable and forget your sadness.
See a doctor. If your sadness starts to interfere with your everyday life seriously, you should ask your doctor for help.