I've been trying an experiment. Particularly when I've had a bad week.
I always pop into the shop on the way home to get stuff for dinner. Whilst there, I'm making a point of smiling at everyone that serves me and wishing them a happy weekend.
It works wonders. Most of them look gobsmacked, with the look of surprise transformed into a lovely smile and usually a greeting in return.
So I feel better and hopefully their day is a little nicer, too.
The best things in life really are free. Sometimes.