The answer was deceptively simple, and annoyingly right...
Write every day, even just a line or two.
It's important that you're getting ideas and cementing them onto paper/Word. You can babble, rant, question, list, anything you like. It's a start on your way to becoming a best selling author. Even if you start with "I have nooo idea what I'm writing about but some blog told me to because it would help me. Better than that, today at work, Jim decided that he was going to chug the whole water dispenser and it was hilarious...." etc. There's a potential story!
It will inspire you to write about things, to find "your voice". (On my researching travels I also found the tip that if you read aloud for an hour a day, whether it's a piece you've written or a book, you'll really begin to find your voice.)
Write some more.
Push yourself. If you're out of practice with writing, put aside five minutes at first. Then, do ten minutes. Then fifteen. If one day you find yourself with an hour of spare time to be killed, murder it with some brilliant writing. Spend some time planning a story if that's how you write, or free write. As long as you make a habit of it every day.