I have to monitor my mood because I'm prone to depression so I have to nip it in the bud. This is what works for me.
1. Exercise, especially intense aerobic exercise or weightlifting.
2. High-quality canned tuna (due to the fish oils). If/when I get down just having a bit here and there can perk me up.
3. Sauna. It's difficult to be depressed when you sweat it all out. Also gives you time to meditate and get into a better mindspace.
4. "Doing" rather than thinking. For example, trying to get involved in a tasks at home or at work that keep your mind off things. Decluttering, cleaning, gardening, etc. Anything other than negative thought patterns.