So far I've gotten all of my commendations as a DPS, so I don't think we'll have difficulty getting any.

That said, I'm not sure why I got so many to be honest. I simply said "Hello" at the start of each Guildhest/Dungeon and did an adequate job for the most part. The only one I feel I deserved (and I hope the tank got one, too) was my last run of Pharos Sirius where the tank and I explained the fights to the new guys. I ended up giving my commendation to the healer because he did a damn fine job during the Siren fight, although the DRG in our group was just as excellent.