Dictionaries list two pronunciations for you're, a weak pronunciation and a strong pronunciation. In which situations do we use the strong version of you're /jɔːr/, and in which situations do we use the weak version of you're /jər/?
Use the "strong" version when speaking slowly, speaking for clarity, or when emphasising or contrasting the word you:
Use the weak version when the word is not stressed, when speaking quickly and when "you" is implied by the context.
I'm going shopping. You're going to do homework. No discussion! (/jɔːr/)
So, you're playing tennis tommorrow? (/jər/)
In the first example the contrast is between "I'm" and "You're" so these words would be emphasised. In the second there would be no need of emphasis (the word "tennis" is more significant) and so naturally unstressed words are reduced.