I found that starting each day with saying something positive to myself and then going out the door each day wearing my "Clown Face" is what keeps me positive. By clown face I mean that I only show the world what will make them smile or feel happy! By doing this eventually I feel happy.
This does not mean putting on makeup like a clown - just resolving to put out good vibes and a smile so that all others I come in contact with will in some way or another feel good that they saw me. This is an old technique that my father taught me.