So the three blessings exercise demands that you focus your attention, as you end your day, on three things that went well and why they went well. These three don't have to be earthshattering: they can be as small as a beautiful flower you looked at. This re-educates your attention toward the positive. Even severely depressed people can find three things that went well every day, and when they do, their depression may start to lift.
What to do:
Every night for the next week, right before you go to bed, write down three things that went really well today. These things can be small and ordinary in importance. Think about why this good thing happened.
Once you have completed your list of good events and your explanations for them on any night, pick one good event that you would like to dream about. Positive dreams increase life satisfaction and consolidate the memories of good events, so it is worth the effort to try and influence your dreams.
Doing the following will increase your chances of having a positive dream:
Give the positive event a name
As you go to sleep, say the name over and over, visualize it, and intend to dream about it
In the morning write down your positive dream.
Note your mood when awakened in the morning.