If someone does something to stand out, I am more likely to see them as deserving of my commendation. For example, someone who goes out of their way to explain a fight will get my commendation. Likewise, good attitudes will get a commendation. Using a LB at a good time, or raising a party member when it's needed, or pulling some stunt that prevented a wipe... these are all things I notice. Granted, it IS hard to see when a DPS is doing a great job UNLESS they do something exceptional. Oh, and I do enjoy giving out commendations to people who admit they are new to a fight but open to advice. Even if they make a few mistakes, I think we should encourage honesty and good attitudes.

If it's a dungeon where people don't do anything exceptional and don't really speak at all, I'll usually throw it to someone who says 'thanks for the group' or something similar. If no one does that, it'll probably just go to someone random. I very rarely DON'T give out commendations, unless the group was seriously that terrible or rude.