My first rule about any attempt is to be positive. Avoid the dark side and use the force (Luke).
- The geared group will be fast and need hardly any healing. This group is fun, because you can see how much damage a Big Healer can output. Pop the wings whenever you can, make sure you have Shield of the Righteousness on a key bind to use when everything else is hot (waiting for cool down). The tank in this group might get bored and start pulling insanely large groups. Be ready to switch back to Big Heals when this happens. I had a tank pull every mob in the first Protodrake room of Ramparts once.
- The geared damage versus under geared tank (usually a DK!). This happens a lot now, because everyone is looking for a shorter queue time and switching to a tank spec gets you that. This group will have your Big Heals flying as the tank won't be able to hold aggro and the DPS will end up tanking. It's more like raid healing since you'll be bombing heals on everyone. Hand of Protection can be very useful in this group. I sometimes mark a Skull and X in pulls to help the tank and DPS coordinate.
- The under geared group. I get these groups a lot. Their alt just made level 80, and they jump into heroics immediately (who doesn't do this!). The damage per second is less then 2000, if not worse. The tank needs constant attention to stay alive. I can carry this group with my Big Healer, but I feel sorry for a new healer when they get in this group. Encourage the tanks in these groups, give them props and back slabs aplenty. The more tanks in the dungeon finder the better.
- The slow tank group. Can be any of the above groups, but the tank seems to be preoccupied and the pulls come slow. The party might get impatient and start pulling just to get the tank to move faster. Healing can be challenging if this starts happening. I like having a two-monitor setup, so I can be browsing the web when things get slow.
- The timid tank. This like the above group will be slower. The tank will ask if everyone is ready before every pull. They will diligently mark up every mob in the next pull with a kill order. The healing in this group is usually easy and boring. Like first group, I can usually add some damage of my own into the mix.