Mages can get away with wearing some pve pieces if you dont have access to full pvp gear yet. You're pretty much going to want to find either a rogue, dpriest, spriest, or ret for 2s. RMP (rogue/mage/dpriest) or shatterplay (resto sham/spriest/mage) are your best bets for 3s comps. And yeah, as stated above, you're gonna want to focus on purely control until your team is sure they can get a kill on something.