Don't be afraid to play a character as "appropriately stupid". Just because you know the powers and weaknesses of a certain monster or the general plot of an adventure, doesn't mean your character does.
For example, in our last session, we found ourselves up against a Rakshasa with some sorcerer levels. He was kicking the crap out of us. Sure, I know the old blessed crossbow routine, but my character's Knowledge: Planes check said he didn't. I could have just metagamed it and used Align Weapon on my crossbow and laid into him, but I played "appropriately stupid" and forced myself to come up with some other method.
As it was, I cast Silence on the party tank (see my sig), who proceeded to grapple the Rakshasa. Nearly the whole party joined in, wizard included, and pinned him to the ground and choked him to death. I think that makes for a much better story than, "I blessed my crossbow, pegged him a couple times, and looted the body."