I really like an expansion of this idea that I heard somewhere awhile back:

Keep a few significant problems in your mind...and also keep a few significant solutions / problem solving techniques in your mind. Then when you encounter new problems, check them against your set of solutions and see if any of them apply. Also, when you encounter new problem solving techniques, check them against your set of problems to see if they're applicable. Whenever you encounter a new problem or solution that seems unusually significant, add it to the list that you keep track of