1 Change your physiology.
Act like you feel good. Make your face reflect the emotion you want to feel. Smile, and make it reach your eyes. Breathe deeply, slowly. Sigh happily. Sit up straight, shoulders back in confident posture. Your body tells your brain how you feel. Change your physiology, and biochemistry will adjust.
2 Free your mind.
First, you need to be aware of how you are thinking. Are your thoughts full of insults and profanity toward yourself or others? Are your thoughts reflecting a "can't do" attitude? Are your thoughts trapped in an anxious spiral of doom? If your thoughts are negative, they are hurting you. They are trapping you. Free your mind by thinking in a new way. Instead of blaming how you feel on the actions or inactions of others, decide that your emotions are your responsibility and that you will decide how you feel from this moment on. Then ask yourself what you need right now to feel better, what you can do for yourself right now to improve your mood.
3 Nourish your body.
Drink some water. Eat a piece of raw fruit or vegetable - a food most nourishing to your cells. Take a nap. Let the sun shine on your skin. Give yourself a massage. Take a shower. If you are neglecting your body, your stress hormone level is too high. Taking care of your body lowers it, and improves every aspect of how you feel, physically, mentally, emotionally.
4 Entertain yourself.
Read, Listen to, or Watch something that always makes you feel good or laugh. Go to youtube and watch funny or inspiring videos. Make a happy or silly or peaceful play list on your computer or mp3 player. Read a funny book. Watch your favorite feel-good or funny show or movie. Here are some of my favorites: Uplifting News, How To Create Big, Owl City - Good Time, Glad No Matter What by SARK
5 Get off of your butt.
Right now. Stand up. Shake it off. Get your blood pumping with some light aerobic exercise. Step away from the computer. If you are feeling down, do things to crack yourself up - move in a silly way, dance like nobody's watching, make faces at yourself in a mirror, strike a pose. If you are feeling anxiety or apathy, do an angry dance. Kick the crap out of the floor. Punch your mattress until your arms are too tired to move. Jump up and down until your heart is pumping and you need some water. Go for a walk, jog, or run outside if you can. Do it now!