It has to be a consistent practice for it to work, but it does work. Start each day (or early in the day do this) by thinking of three things for which you're grateful. They don't have to be profound. Example:

1. Got beers with buddy before his family takes a month-long vacay
2. An app that I like recently released a new version with enhancements and new features
3. Building mgmt offered some free rent for lease renewals during the same time we'd be renewing anyway

Try it. It works. But it took a fair amount of time to feel natural and easy, at least for me.