I'm reading Seeds for a Boundless Life by Zenkei Blanche Hartman. It's a nice and simple book. In it she recommends smiling...not a big inane grin, but a small smile.
Now, I've heard people recommend this before and have always run a mile from that advice: Zen, for me, is all about being exactly how you are right now, not forcing yourself to feel something you're not. But, Hartman is lovely, so I'm giving it a go.
A very small smile whenever I remember. And it does something, that's for sure.