"So, what are you actually doing?"

I find this question invaluable in running Fate.  Almost any time I hear a player doing something in just pure game mechanics, I ask this question.

Same with invokes on aspects.  "Okay, great... what does that actually mean in terms of what's happening?"

It's one of the main tools I use to keep things in games focused on the fiction, and not on the character sheets and dice.