Challenge your thinking on a regular basis.
It's okay to get all the information, check your facts and explore possible outcomes. It's good to bounce ideas off your co-workers, engage in a fact-checking mission, do spreadsheets with pros and cons and sleep on it.
But once you get past all these necessities, it's good to think outside the box. Challenge yourself to move your thoughts to a different place. Contemplate something you've never done before. Question your assumptions. Find out why you do what you do, what worked before, what failed but seemed to have promise.
See, just because something is over doesn't mean you can't still learn from it. It may have been a humiliating failure or a roaring success, but there are still lessons to be learned. Re-live it, and re-evaluate what made it that success or failure.
Contemplate how you can do things better. Contemplate how you can take the knowledge learned in a whole new direction. Contemplate synthesis and re-organization. Think about consolidation and cutting away the fat. Whatever needs to be done, contemplate on those things.
Challenge your thinking. Truly think outside the box and see what new combinations will occur!