"You and me" is correct when it's the object of a verb or preposition.
* Example: The teacher gave you and me a good grade. (You and me are the objects of the verb "gave")
"You and I" is correct when it's the subject of a verb.
* Example: You and I should go to the movies. (You and I are the subjects of the verb "should go")
Here's a simple trick to remember:
* If you can replace "you and me" with "us," then it's correct.
* If you can replace "you and me" with "we," then it's incorrect.
Let me know if you have any more questions!