I often give my comms to dps (if they stick around long enough for me to commend them) - DPS usually have to wait longer for queues so I feel it's a good way to reward them for it. (Especially if they have to deal with my casual-playing-ass in a party)
If they don't act like a d!!k, don't pull before the tank, keep out of easily avoidable AoE's (unless they are sprouts in which case it's acceptable), not go afk without reason, be funny/chatty/polite - I'll give them comms.
If they have an awesome glam - I'll give them comms.
If they have a cool/funny name - I'll give them comms.