I think you best bet is to tell him to look at the guide http://www.tankspot.com/showthread.p...rty-Arms-Guide. If he reads that a few times and puts the ideas into practise his DPS should go up nicely.
I'm not familiar with the fight in question, but I didn't see any slams (probably because he's not specced into improved slam) so I don't think he's aware of the priority system to use. I only saw one Heroic Strike in two logs. Heroic strike is a good rage dump that doesn't steal a global cooldown.
His spec is a little strange. 5/5 defelection is not much use for a DPS spec. The guide's specs are a good starting point.