I started winning ALOT more in Arena. I was pretty dissatisfied with the fact that my most frequent rankings were 3-2/4-2, with one or two 6-2s. I then read this guide:
http://ihearthu.com/vivafringes-guide-to-arena/ and though some of it's a bit outdated already, there is some excellent advice.
Basically the core of what I did wrong, was that I went to the face WAY too often, instead of trading off my guys. My logic was that I would go to the face, then opponent would trade off, so I got a net gain. What I wasn't seeing, and what is now clear (I've really started noticing it), is that often not trading will offer the opponent the chance to cast a buff or trade more favourably with a Charge minion or whatever. So basically, I'm now playing ULTRA-safe unless I'm trying to kill my opponent fast.
Anyway, guide is good. Also contains Trump's advice on picks, which I roughly agree with. I also like Mage more now than I did before, mostly because I valued some cards too high and some too low, resulting in me being bad at drafting Mage
I still hate drafting Priest and Warrior, and more and I avoid Shaman.