Age. Without question, age has improved my problem solving abilities. I no longer expect to come up with an instant solution; instead I get to know the problem as best I can, then go and do something else. My subconscious will eventually deliver the optimal solution.

Interestingly, "eventually" usually means in the shower the next morning. From that I assume that I'm more receptive to flashes of inspiration while I'm relatively relaxed in the shower, and also that the real work of finding a solution happens while I'm asleep.