Each day, write down three things (events, experiences, interactions, etc.) that you think went well or that you appreciated. These can be small things like something about nature you enjoyed, a pleasant interaction with someone, a good meal, or even feeling good about the way you responded to a stressful situation.
Also ask yourself why you think these events occurred. Often these experiences are unplanned, but they might not have registered in your consciousness unless you had a mindful intent to notice and appreciate them. See how this affects your mood and outlook.