When people say "in here", it tells me they are physically inside something (eg. a room or a box). I understand the confusion, because while a student may say "I'm living in Brisbane", it's grammatically incorrect to then say "It's nice in here." I heard this a lot. In this case, "in Brisbane" should equal "here". "I'm living in Brisbane. It's nice here."

Use "in" when you want to say that something is "in" and not "at", "on", or any other place. All these small common words are in the book "keys to words" at: http://www.keys2words.info/