The single most useful piece of GM advice I've yet read is Dr Rotwang's Adventure Funnel.
The Adventure Funnel is a quick and satisfying technique for creating nuanced and memorable adventures. Start with a goal, throw in some obstacles, season with details (I think I'm getting my metaphors mixed...) and the result is a stew of ideas that hang together loosely enough to not be binding, but are well-interconnected enough to run an adventure that looks, at the table, like pages of carefully-written notes. The key is throwing things at the wall (or page, or pot—as the case may be) without worrying about vetting it or making sense of it first. Something nonsensical you put down might inspire an entire plot thread that turns out to be brilliant. Once inspiration strikes the connections just make themselves, and the Adventure Funnel is nothing if not good at generating inspiration.
In my first attempt using the Adventure Funnel (and so far only, I should take my own advice and use it more), one of the silly things I wrote down when I couldn't think of anything was "And then: DRAGON ATTACK". It turned out to inspire one of two major villains that injected some delicious pathos into the adventure. Yes, a dragon attacked, no, the player didn't fight it, and the fallout from the dragon's actions (demanding a yearly ransom, killing the villiage elder, shaming the hubris-filled priest) is still being felt in my ongoing Edge of Empire campaign. In fact, the major reveal and cliffhanger from the last session is a direct result of the spiritual crisis of that shamed priest.
So, go read The Adventure Funnel and get cooking up something fast and tasty for your next game.