One of the best pieces of advice I’ve ever gotten was if you want to get good at something, Keep your tools with you all the time. A writer should never be without something to write with. A photographer should always have a camera. A musician should keep their instrument close and so on. While this is probably easier for a flute player than a cellist, it should be even easier for a writer. All you need is a pen or pencil and a small notebook. Or even just your phone (I wrote the draft of this on Google Docs on my phone on the subway).
Having something to write with allows you to be prepared to write anytime you have a free moment, or to capture the ideas that flit through your head. Keep it by your bedside; tuck it in your purse, bag, or pocket; live with it as much as you can. Just having something at hand can be an inducement to write.
What you put in the notebook is up to you. I fill mine with a mixture of journaling, frewriting, quotes from books I’m reading, notes for blog posts, thoughts, sketches, and scenes for whatever I’m currently working on. I’ve gone through three notebooks since starting this habit. A fourth is filling and lives with me nearly constantly, though I always have my phone as backup.
A note about ideas: Write them down as soon as you have them. Trust me on this. Even if they are half formed little things, barely two words and a sneeze. Writing down thoughts makes them suddenly concrete. They gain weight and start acreteing other ideas – like suns forming in a nebula. Major ideas gain little ones like planets and moons. Pretty soon you’ve got a whole system whirling around, or even a new universe, waiting to be captured in writing. But forget to write down the idea and it pops like a soap bubble, destroying the potential before its even begun. The best ideas are the ones we forgot to capture. You’ve been warned.