Probably no attitude is more essential to mental and emotional well-being than that of gratitude. A practice of focusing on the man reasons we have to be grateful rather than on the things we don't have or can't achieve is a soothing balm. 

If one makes it a practice, as I have, albeit somewhat irregularly, to begin and end the day by mentally listing those people, circumstances and things for which one is grateful, they will be well on their way to contentment and the happiness it affords.

How and what we remember also has a role to play.

It has been said that we should write the things done against us in sand and those things done for us in concrete.