Sometimes a raid leader will require the pally to become the dedicated healer of the group. This is not going to be too often, pally heals do not match what a cleric, a shammy, even a druid, can do. But when push comes to shove, we do have some healing abilities.
First off, when you are the group's healer, do not even try to dps. At all costs you have to keep yourself alive so you can heal everyone in the group. For that reason, no stuns. And, no agro spells. You are healing, not dps'ing and the group will depend on you to keep them alive.
So, what should you have?
Automatically, you need Splash. Get and have the strongest splash you can get. This is not so much for it's healing ability but for its curing ability. Yes, it does have a nice heal too, but the curing ability (unless you have overlapping pallies) is what you need for this. It helps to cure just about everything. That, plus the heal effect, makes it invaluable to the healing pally.
Now, you need heals. Group heals and targeted heals. Quick and slow. Do know that the quick ones cost more mana so be stingy with them. But remember, better to use a quick heal than to lose a person in your group. So have Wave of Grief (or successor spell) for your main group heal and Aurora of Dayspring for your quick group heal. Also, have Ardent Touch for your main targeted heal and both Burst of Dayspring and Blessed Light for your two quick targeted heals. Do have all 5, you will need them.
Also, there is a duration heal. Ardent Cleansing is the one you want, at least till you get past level 105. I find it best to use the duration heal on side people who do not get much damage.
Now, the next spell is one that is not a heal whatsoever. It is a DD spell, but it has a single use. Brilliant Vindication allows you to cast the next spell as a double cast. So if your group is getting weak, cast Brilliant Vindication on the mob then cast the group heal. You can all but double your healing.
You also need the cures. Along with Splash, have Ardent Purity up, it is great against poisons, diseases and curses. Depurate have only if you need to cure corruption, which could be any raid so have it. There are others but unless there are specific, pressing reasons, tis best to ignore them.
Finally, there is the one that you need as if you were meleeing -- Protective Proclamation. This you want to cast on the mob. Why? Because it heals the tank and gives him a nice, temporary AC buff.
That gives you one and only one spell slot left. Use it to cast a buff, mainly Brells, but think also about the Aegoism spell.
Now, abilities. There is one ability that, when running right, lowers your hatred. Marr's Salvation. Have it up and use it on yourself and anyone who you do not want getting agro. It is not a guarantee, but as it does lower hate over time, it can help a lot.
