As a Tank I generally commend the healer or when I see a dps going nuts on aoe for mobs/single target for bosses. Also if the DPS goes out of their way to help others it means the world to me. Like as a PLD if i'm spamming Total Eclipse and running low on TP when I get a Goad or Tact(without asking for it) it makes me smile and consider giving it to them.

Like if you want a fantastic example of something like this last night I was running the Burn as a PLD getting up my flashes before I switch to Sword and a BLM in my group Mana Shifted me to give me back MP. I was floored by this since I always play WAR/DRK and have never seen this happen to me before but I was extremely grateful as my party was all casters. That BLM secured my comm right then and there.