I keep a notebook next to my computer on my writing table. A simple, black, Moleskine, ruled 80 page journal – they come in sets of three.
Into this notebook goes an entry for every day. During my daily writing I sometimes start by making a note, but at some point during that day’s writing session I always turn to it and scribble.
I write my frustrations and hopes about my work, approaches I’m considering, things about life that are distracting me or making it hard to write. I often jot in the top margin what time I started writing or a reminder to revisit that page later to review important notes.
If I go to an author reading this is the notebook that goes with me so that I can capture ideas or comments that come during the evening.
The Commonplace Book is a working journal. It is a place, at my elbow or under my arm, where I can park whatever is standing between me and the work I’m trying to get done. I’m in my 17th notebook. Some days there is a page, other days a line, but it has become essential to my creative process.
Sidenote: The Wikipedia entry on Commonplace Book is surprisingly robust. The history of this tool is richer than you think.