Here's a list of what has gotten (+) my comm in the past and which ones have not (-)

+Had a spat with another member. Gave comm to the peacemaker.
+Friendly player
+Does their job well, but not a dick
+Healers who dealt with my dumb ass when I was having an off day with mechanics
-Comm beggers
-Dicks
-Derps. We all have our off days. Just be willing to accept you won't get many comms that day.

As a side note, today in my LLR, I got the Aery. I wasn't sure who to give my comm to, and we were already past the instant wipe mechanic on the last boss. NIN goes down and the healer's raise macro had a line in party chat, "You've met with a terrible fate." Majora's Mask reference got my comm. Ironically, the healer may not have gotten that comm had they done just a bit better keeping the NIN alive.