About a month ago I came across an inspiring book on brainpicker's twitter feed called "An Illustrated Life: Drawing inspiration from the private sketchbooks of artists, illustrators, and designers", by Danny Gregory. It's a real gem. I'm always drawn to things like this, which give a glimpse into the creative process. An analog of this for films is the commentary one can often find on a DVD, where a director or actors discuss the kind of meta ideas that went into the creation of the film, the development of the plot or a character, etc. This book covers about fifty artists, and includes samples from their sketchbooks, and a short essay by each describing how they use a sketchbook and what it means to them.
A few things that stand out so far (I'm about 3/4 of the way through it): I like that they often share humble thoughts about their view of themselves as artists, basically things I can relate to as I try to get started keeping a regular sketchbook: things like how difficult it is to start sketching on the first page of a fresh new sketchbook, for fear of messing it up, or being timid to sketch in public and have people watch. That part reminds me of the down-to-earch discussions that Frank Ghery has with Sydney Pollack in "Sketches of Frank Ghery", in which he confesses his lack of confidence.
One of the things that drew me to the book is that I have been wanting to get back to drawing, which is something I did in high school, but dropped when I went to college. What I like about the idea of drawing is that it seems like a good exercise in meditation, and that it would nurture one's observational skills. The artist Rick Beerhorst articulates this really well: "Drawing is a sort of drinking in of the sensory world. It is also grounding because of the quiet concentration. The stillness is like meditation or study."
It's also really useful from a more practical standpoint of surveying different artistic styles and methods. One recurring style I really like is the mixing of different media, in particular ink with water color or pastels.