The following TEDx talk is funny and interesting. Even better, it has some specific ideas about how to change our lives. Shawn Achor says that if people write down three things they are grateful for each day for 21 days, then it changes their optimism. (Starting at 11:01 in the video.) I do not believe that I am a pessimist, but I will admit that in my situation the difference between pessimism and realism is very small.
As I have written about before, psychology has proved that a healthy mind is a delusionally-optimistic mind. Even if I am not a pessimist, I am certainly not a typical–healthy–deluded optimist. I would like to be, though. Therefore, a few days ago, I started this exercise, and I do not see why it will not help me.