One of the sports radio programs I listen to is what I would call a shit talker. You know the type, the people who just throw crazy ideas and hope something sticks to the wall.
As strange as it seems, there is something to be learned from that behavior that applies to many D&D campaigns.
My campaigns tend to be hard. Yes, combat is difficult, but that's not what I mean. My villains are not static, they adapt to the PCs. If the PCs defeat a villain a certain way early in the campaign, you can bet that he will take steps to ensure it doesn't happen again.
More than that, my campaigns require thought. I will often place hints and hooks throughout lower level adventures. Those that my PCs seem to latch onto, become the next tier of adventures. I am loath to waste a good hook, however, and often will use "missed hooks" as ways for the PCs to gain advantage over difficult situations.
My group of PCs are acting on behalf of a local magistrate, undertaking missions for the crown. As time moves on they slowly uncover evidence of a coup attempt.
At the mid level, they find that this coup has the backing of several powerful military members and some factions in the government. They ignored the chance to track a messenger back to his origin, however. This could have armed them with knowledge of a draconic presence in the coup.
At high levels, they confront the leader of the coup as he moves against the king. The PCs were prepared to fight a powerful caster, not the dragon that revealed himself.
This is, by necessity, an overview and oversimplification.
My PCs could have become more prepared by tracking the messenger, or a host of other hooks during the campaign.
This was a great example of one of my other favorite tactics in DMing. The PCs will often tell you their assumptions. Let them be right on occasion, but make sure they are wrong at times too.
Overall, the PCs should have options, even when they don't.
I'll have to expand on that sometime in the future.
Take care and have fun.