You say you can't cheer others. What is cheering ? How can someone change other's mood ?
One of my dear friend once told me that she doesn't know how to cheer up people. 'Mujey logo ko manana nahi ata.' If someone is sad or depressed around me then I just leave him/her alone.
This was one of the most unorthodox thing I had ever heard. Normally people try to console or help the depressed person so that he or she can sail over such grim. Other's try to share their sorrow and show that they are there for him/her.
She might sound unconventional or a cold hearted girl however she is not. She does not console anybody because she fears that she might worsen their mood rather then making them feel better. She just doesn't understand what to talk or say.
So she leaves that depressed people alone, thinking he/she will recover sooner without her. I believe, sometimes only an attempt of a friend gives boost to a person feeling low.
Sometimes even the simplest thing acts as healing agent. If you really care for that person you will be able to lighten their hearts. Here I m not talking about mood swings where sometimes people want to be alone.
My friend Just ask yourself one thing if you are depressed or you are feeling low will you not want your dearest friend to come up to you and cheer you up? Will you like them if they ignore you, if they stay unaffected or they leave you alone when you are sad or depressed.
If no, then try to cheer up people you care for. Because in life what you give is what you get.