The use of are vs. is can be something that confounds people and is one of the most common areas to find typos in documents. Many writers have fallen victim to this, it usually occurs when going back and editing some text and then neglecting to update the rest of the sentence properly.
The most common guideline to use is to assess the context. When discussing people you should consider whether the subject is plural or singular. When singular you would use "is", i.e. he is, she is, It is. When plural you would use "are", i.e. they are, we are. Whenever you happen to be discussing something that is plural in context you will likely be using "are" as opposed to "is".

The tough thing is that there are examples that appear to break the rules, that's one of the fun (or annoying) quirks of the English language. "You are" is the correct statement, even though the subject is singular. It can be argued that "you" can refer to multiple individuals so the grammar holds up, but in most contexts we would you "you" to refer to a single individual. Sometimes it really helps to actually say what it is you have typed, saying something out loud often quickly sounds either right or wrong.