(it's not wrong to be blue, however, it won't help you much for long)
Think positive.
Give an animal some love.
Believe in your dreams. Look forward to them.
Swim.
Sing. Loud!
Hug.
Know that you're beautiful, loved, and important.
Eat something delicious!
Don't get hung up on being perfect (or having something be perfect)!
Watch a movie you haven't seen in years.
Learn a new skill.
Draw something silly!
Exercise - 100 sit ups. Now! Well, maybe not that many...
Go for a bike ride.
Spend time on yourself.
Say thank you to someone for something you may have taken for granted.
Make something for someone else.
Watch the clouds go by. Try to pick out shapes and animals!
Clean your room up a bit. Or more than a bit, because it probably needs it.
SNAP OUT OF IT, DOOD!
Drink some chamomile tea with honey and milk.
Listen to some smooth jazz or something!
Call a friend :-)