Guardian's 101

General

1. We rock the party
2. Guardians are tanks. Heavy armor and aggro management.
3. Instances usually go better if you let us control the pace of the exploration. Please don't start pulling mobs unless you're asked; that's how fellowships wipe. If we stop, there's usually a good reason.
4. Many of our attacks are reaction chains which require us to be getting attacked by the mob.
5. Keep us healed. Although we can heal ourselves a little, our power is better used to keep aggro.
6. Our Repair bills are a lot more than yours. Contributions are appreciated.

[edit] Aggro

1. Hunters especially (who do lots of DPS at range) should hold-off on using their best attacks until the Guardian has locked aggro (usually when the mob is under 60% health). If you're pulling too much aggro, please use your Endurance stance and Beneath Notice.
2. Unless pulling on purpose, we prefer other players to only attack the mob we (either the Main Tank or the Off Tank) are attacking. If you attack another mob, you risk pulling aggro. Everyone attacking different mobs can make the battle last far longer than it should.
3. The wavy red lines above a mob's head indicate we have landed a move that generates a good bit of aggro. This may be useful to watch for if you are waiting to deal out full DPS.
4. Don't run from the tank. It's the absolute worst thing you can do, and everyone does it! If you are getting hit, don't run around like an idiot. Stand still, and we will come to you. Better yet, bring the monster to us! Whatever you do, don't run away from us, and don't run in circles.
5. If you tend to pull aggro a lot, or if you are a Minstrel: SIT IN THE POCKET! The pocket is an area directly behind or to the side of a Guardian where you are out of reach of attackers, but the Guardian can easily turn and regain aggro.
6. It is FAR more difficult to "steal" aggro and pull a mob off of you, than it is to get & keep aggro to begin with.
7. Often guardians will use our various AoE attacks to try to build up at least a little aggro on all the mobs present. If you are a class that can mez or root, please let us know ahead of time so that we don't let loose with a swiping attack that will knock out of mez the mob that you just mezzed half a second ago without telling us.
8. If your mez breaks, please let us know whether we need to attack that mob or leave it alone. If you plan on re-mezzing the mob, move away and THEN re-mez. That way our AoE attacks won't cancel your mez. If you want us to pull aggro, position yourself (and more importantly, the mob attacking you) in front of us. That way our AoE skills will hit it.
9. Some good information about aggro management: http://forums.lotro.com/showthread.php?t=55821

[edit] Miscellaneous

1. Acorns are items that allow you to call the Guardian to you. We can make them at level 38. We can make lots of them, but you can only carry one acorn at a time. The guardian cannot be summoned into (or out of) an instance. Acorns can be mailed, so you can effectively fed-ex a guardian to you if you're both near a mailbox.