Me and friend play team doubles every day for at least 3 games and seeing how the better you play the higher your 'rank' is, we usually shoot for a 3 game average of 1500 or 1600 a day. Though there are a few problems I have ran into: 1) The only way it seem both of us can get a good score is if we trade off how many kills we get during a game. Just say we are playing absolute noobs; I find it really strange that we have to decide which one of us get the the 20 kills and which one of us get the 5. When we both play as well as we can we come out to be about even (12-13) (assuming we are not getting owned) and we can never get above 1450 when we do this. 2) It seems that the whole "MATCH MAKING" idea is completely out the window for reach. I am constantly being put up against either terrible halo players or Halo gods, and rarely is there an in-between. Sure, they are a major and i am a major, but the ranks in this game seem to only explain how much you play the game and not how good you are. I want to be pitted up against people on my level, not random levels. Does anyone understand how the ranking system works? I noticed that it starts at 1000 and increases with ever kill you get and decreases with ever death you get... But that is my only understanding of it.
thats basically it in a really simple form. bungie posted the formula in one the updates, and its complicated, and i cant remember most of it. i remember it involves some form of a sine curve. assists are taken into account as well i know. and your matchmaking rank (major, captain, etc.) is not taken into account at all for who you are matched up with. im pretty sure its based almost purely on your party's trueskill rank.
Ladnil made a thread about this during the beta, some of the specifics of the calculations may have changed since then but even if they have, it's still largely accurate and a very useful explanation of how things work in Arena (first and foremost being that the daily rating you're worrying about basically means nothing in terms of how you're ranked). You can find the thread here.