DUDE CHAIN HEAL IS AMAZING, it is worth the mana it takes to cast even if it is just hitting 2 targets (I hope you realize it is buffed up by 30% with our talents)
Now you didn't have a link to your character in this thread (maybe I missed it) but I don't know what your healing looks like but I assume if your friend said you are well geared for it you have about 1400 healing which is plenty.
Just put Earthen Shield on tank, use Healing wave and Lesser healing wave depending on situation, but if the dps take dmg use chain heal on them it will bounce to tank if they are still not topped off target tank now and chain heal this works pretty well. Now if the dps pulls agro then you have to spam Lesser Healing wave on them to keep them up, hopefuly they have some way to drop agro though because you may have to just let them die otherwise.
Shattered Halls is an intimidating instance but all its takes is knowledge practice and skill. If your making mistakes or having trouble on certain parts you can go play this on regular shattered halls, while it will be much easier you can do a pull and say man these guys hit harder, hey this room is tricky cause you can double pull, or you can see where all the ninjas are hiding (there are a few spots and some are not always there). That covers knowledge and practice, skill is really you just knowing how to heal, I almost never use either of my healing wave spells on a dps, chain heal is amazing i love when they are taking damage i can just start spamming chain heal, if there are AOEs and Cleaves CHAIN HEAL. Chain Heal is ridiculously Over powered, the only reason it has yet to be nerfd is it is no good in arena, but in pve it is just outstanding.
This also may sound mean, but know your limitations, if a dps keeps pulling agro while you have a paladin tank the pally is either A. under geared or B. stupid dps. If a rogue or mage or whatever it is keeps pulling agro, let him die a couple pulls, because you could switch to him and spam heal lesser healing wave on him but unless your Earthen shield ticks for about 1k your tank can't take too much abuse for long and this dumb dps is putting you and the group at risk.
So ya practice, learn to use chain heal it is OP, and let stupid dps die! NOW YOU KNOW HOW TO BECOME AN EPIC SHAMAN HEROIC BADGE FARMER!!! GO!