Be social. Be with other people and interact. Listen to music by going to a concert; all these things help increase the bodies serotonin levels, a natural anti-depressant. Lastly, do a good deed or an unsolicited act of kindness. Recent research has shown that happy people are at least 50% healthier than those who are not happy. Doing good deeds for others will come back to you in good health!
Walk until it is difficult to talk to yourself or your walking partner. Then you know that you are working your system and producing a constant cardiac output. Walk for at least 30 minutes, most days of the week.