You need to create little situations which cheer you up - buy an ice cream, go riding, hire a bike, visit your local Old Folks Home and chat to people there.
Look for some volunteering - do some weeding for a friend, neighbour. Ask if you can cut the grass.
If it's dark, Go guerilla gardening and plant some flowers. You'll smile every time you pass.
Join a choir, campaign group, drama club.
Obviously we don't know what your particular problems are but everyone has them. You will lose jobs, friends, family in this life. Everyone does. Some people are better at ploughing on and not frightening the horses. This is what need to try and develop too.
Smile to everyone no matter what you're thinking and most will smile back.