Your / You're

I had a whole plan of what the next few blog entries would be; however, I received an email that changed this objective. (The subject line of said email will be included in my examples below.)

The subject of this blog was going to be covered in a few weeks, and it would have been grouped with a few other rules. This shall be no longer.

I will present one that should be obvious to all, but for some reason it's not.
Your = Possessive
You're = You are

This is really simple and should never ever be confused. The best way to remember it is that the "re" in "you're" is the word "are" with the "a" cut off.

If one can replace the word in the sentence with "you are" then use "you're"… it's as easy as that.

For example: "You're late for dinner."
That means, "You are late for dinner."
Alternatively, "Your dinner is on the table."
That means "The dinner that belongs to you is on the table."

When one says "your" in place of "you're" the confusion is astronomical.
For example, "I believe your offended."
My response would be, "You believe my offended?"

Conversely, "I have taken you're phone."
My response would be, "You have taken I am phone?"

Finally, "This dog is you'res"
My response would be, "Go away, and read a grammar textbook."
("You'res" is NEVER a word)

You're really going to have to learn your grammar.