I give commendations to whomever I feel deserves it, be it the tank, the DPS or the healer(If I'm not the one healing, or it's a full party dungeon), if someone begs for it, it's an automatic no from me.

I personally don't care one way or the other when I get the achievements, so I rarely go out of my way to try to do things to get people to give me commendations, I just do my job, explain things for new people, because, you know, it's the smart thing to do, the more people that know how to do things, the larger a pool of good players there are to do them with! I'll chat and joke around at times, other times I really just don't have much to say.