Generally I comm people who go above and beyond.

For DPS, those who use peleton automatically get a comm. Other things like feint I also notice. Or the occasional range that will make sure to move and give melee a safe spot, etc.

Tanks who alternate throughout their toolkit for big pulls (ie. Arms length, reprisal, etc) to make the ride smoother.

Healers who work hard, forced to GCD heal because someone isn't doing their job, have to rez people, etc.

Automatically you don't get one if you're just not using your toolkit, or you're one of those people who run in narnia to get hit by mechanics because someone overlapped your AoE circle by the smallest degree. Double negative points if you're a melee and you do that. If you're standing around and pressing 123 in front of a boss as a melee, I assume you're being lazy with positionals (I know enough class animations to know if this happens). If you're collecting vulns, you're not getting a comm. There's a difference in making a mistake occasionally, and just standing there in the middle of a circle that's been there for 4 seconds.

I'm still amazed by the amount of people who play ranged dps for their mains and NEVER peleton...... *shakes head*