If you think of happy things, happy things happen.
Let go of what’s behind, there might be no remedy to rectify it. And if you are not able to let go you will be stuck in some situation where there is no benefit to yourself. Let it go, shift to the things that makes you happy.
Even things are not smooth at work, complete it. I will go to some favourite place and pamper myself with a meal.
Don’t bring your work home. It’s your free time, do some work-out, catch a movie, see some friend, bring the kids out, work on your hobby, this are all the source of happiness and joy.