I sometimes find it harder to recall happy memories than sad ones. Maybe we’re programmed that way. If I focus, I can think of happy times with my family, friends, adventures, etc. It’s particularly hard when times are tough, but when you take the time to list the good times, it drowns out the bad times.
This is a pretty straight forward exercise. Write down as many happy thoughts about your life and your past as you can think of. For the sake of argument, pretend you’re Harry Potter and you need to produce a Patronis charm (for you Harry Potter fans). Think of the happiest time in your life and write about it.