This is a habit I stole from James Altucher on Quora. Since implementing it into my life, I now have the tough challenge of choosing from too many ideas.
Coming up with great ideas requires muscle--the act of creating actionable ideas stretches and flexes that muscle in a way that keeps it healthy and fresh. Carry a journal with you, or make use of the notepad on your phone and, throughout the day, jot down ideas that come to mind. There is something about writing your ideas down that makes the brain feel like the idea was acknowledged.
Do this for a couple days and you'll see. You'll be swimming in great ideas.