is that YOUR bike?
can i have YOUR tuna fish sandwich?
i hate YOUR annoying face.

YOU'RE is actually two words combined: YOU and ARE. so before you say or type it, split the word into two and see if it still works, like this:

YOU'RE going to the mall.
(YOU ARE going to the mall.)
YOU'RE the coolest person ever!
(YOU ARE the coolest person ever!)
YOU'RE not allowed to have my crack pipe.
(YOU ARE not allowed to have my crack pipe.)

i found a really great place to practice using the correct word:

TAKE THE YOUR VS. YOU'RE QUIZ

next time: TO vs. TOO