It doesn't have to be today-- or even tomorrow, just do something nice for someone; without asking for anything in return. It can be small, or something big and life-changing, but just help someone out, or even tell them they look nice: That can make someone's day. And, if they do want to return the favor, just tell them to do something nice for someone else.

Isn't that rather a mission than something personal?
The idea is nice though.