A year or so ago, I ran into a book about Zentangles. At the time, I rolled my eyes and muttered, "A book on how to doodle? Give me a break!" But, but, but... Over time, I found myself drawn (yes, pun intended) to this controlled doodling. So, I did what most creative people do: I researched it online. What I found astounded me! Instructions and illustrations and so on! I was in creative heaven!
I found this little book and pounced on it. I bought a small package of pens in various tip-sizes and a ream of cardstock. I dragged out my paper cutter (couldn't get the recommended tiles too at the same time I bought the booklet; have since used tiles, cardstock and watercolor paper).
Now, as noted by another, this is not a book of instructions. However, if you do any kind of research about how tangles are created, you can pretty well figure out (have a good eye for) how each tangle is created. As the goal is to relax, learn each tangle separately; literally, just take your time.
The size of the book is pocket-sized (and its description gives the dimensions), and thus perfect for my purse or briefcase. I keep this book, some paper or tiles, and the pens handy for those minutes when I need to take a breather. I'd recommend anyone and everyone with a creative bent to try their hand at this; it takes up less room and is easier to put away than say, jewelry-making or knitting.