Most fights are either about establishing boundaries or frustration/anger over the fact that our mate did not behave the way we "expected" them to under a given circumstance. I believe the healthy approach to fighting is to first use your "edit button". Don't just snap or explode without knowing what it is you hope to accomplish as a result of doing so.
Generally speaking when one person yells the other person stops listening. If you start by asking "Why" questions (in which you have already decided there is not a single "good reason") then you will only succeed in putting the other person on the defensive.
Keep in mind "Anger is the mask that Hurt wears". Whenever someone is "angry" with you what they really are saying is "you hurt me". If you can remember this it is easier to try and get to the bottom of things.
Lastly try to avoid fights over "unknown or unrealistic expectations" and assumptions. If you've never talked about it in the past the other person had no way of knowing you'd feel that "strongly" about it. Also don't make mountains out of mole hills. If it's not one of your "deal breakers" then don't go into World War III mode!
When it comes to relationships there really is no "right" or "wrong". There is only "agree" and "disagree". Ultimately we are all looking for someone who (naturally agrees) with us on the things we consider important. Opposites may attract in the (short run) but it's like that attracts like in the (long run). Since the only person we can control is ourselves we are left with deciding whether or not we can "accept" our mate as they are.
People change when (they) want to change. Trying to (change someone) usually leads to frustration/disappointment on our part and resentment/rebellion on the part of our significant other. In order to be happy you have to (naturally agree) on most things!