Accumulate all the little joyful things that happen to you during the day. They add up. You could keep a journal, and write them down. For example, if there was not bad traffic on the road, if you had a very scrumptious breakfast, if your friend said something uproariously humorous that made you laugh, if you took your dog out for a walk in the park and played with it, add these together. Your outlook can begin to brighten.