Breath

James Nestor explores all the ways breathing, in its various forms, has been used through the ages to improve our physical and mental health. Nestor tries out many of the techniques, and reports on the results he finds, using equipment to document the physical changes he experiences. He focuses on two general groups of breathing forms: forms that are accessible to everyone, everywhere and those that are not. The last chapter of the book nicely summarizes the four ideas that are accessible to everyone, everywhere, and I'll summarize his summary by listing the ideas here:
1. Shut your mouth.
2. Breathe through your nose.
3. Exhale fully.
4. Chew the kinds of foods that require an hour or two of hard chewing a day.
The author also includes a helpful appendix with a link to video and audio tutorials of many specific breathing techniques cited in the book.

I'm trying the four general ideas myself. I'll let you know in a month or two how that's working out for me.