The Practice of Not Thinking, by Ryunosuke Koike

A nifty little book on how to basically compose yourself and behave in a more rational, philosophical way. He gives many useful tips on how to interact more meaningfully with other people, and how to check your own harmful behaviour - behaviour that might not only be harmful to yourself, but to others as well. 

There's a chapter on how to use the internet so you don't get sucked into social media, which would no doubt be useful to many.

It's a short book, some 130 pages that I read while at work. Many of its lessons have lingered with me.