Grammar Nazi:
You're next.
"Your" is a possessive, such as "Your car is on fire."
"You're" is a contraction of "You are". A quick check on which to use is to say the phrase without a contraction and if that is what you mean, use "You're". For example, "Steelers, you are next." makes sense, but "You are car is on fire" does not. For the first example, contract it to "Steelers, you're next." and the second use the possessive as in "Your car is on fire."
