|"I have about five or six random doodles right here."|
I asked this question on Twitter some time ago, and pinned it on my page to see if I could garner some responses. Some people said they just kept everything in their head. Others said that they definitely did, and filled it with various ideas that came to mind. I was originally the former, since I was pretty good at remembering things. Usually I would make a single document with a list of characters, important places, and a synopsis of where my story was going. I didn't start writing until the synopsis was all figured out, though I permitted myself improvisation or adding things to the story as characters and plot elements developed.
Over time, I began to wonder if there would be some benefit in a writer's journal. Finally, I stopped by CVS Pharmacy on the way home from work and bought a $4 pocket journal (because there was no way I was spending $50 on one of Barnes & Nobles' journals). I started jotting down world building ideas, and facts about my current fantasy Work-in-Progress (still unnamed at the time of this writing). I was just collecting ideas, but soon I found that I was enjoying this. I started doodling animals and creatures in my world, and creating maps to help better plan where my characters would go, and what cities or peoples they would encounter. I started sharing them on Twitter, and had people faving, retweeting, and commenting on them. I shared my doodles and notes with my wife, and received feedback from her regarding them.
What I found was my writer's journal became a nice little database to collect ideas that popped in my head or quotes I heard. It also became a pocket sized reference source that I could turn to in my story if I needed to remember a place name or the name of someone important in my world's history. It likewise encouraged me to think more on my world and how it functioned, and what it's history was like. If I had time before work, or I was sitting somewhere bored, I took out my journal and began to jot down any ideas that came to my mind. It got to the point where my journal joined my wallet, keys, and cell phone in the prestigious "I feel naked leaving the house without this" group. It has become a part of my writing which makes it fun and engaging.
Don't worry - I'm in no way saying you aren't a "real writer" unless you use a writer's journal. If you're like some of the people who replied to tweet and you like to just keep things in your head, that's absolutely fine. To paraphrase a Reese's commercial: there's no wrong way to plan your story.