healing wave mostly in 5 mans. Avoid lesser healing wave except as an emergency heal to keep someone alive. like a clothie. Some situations you will find aoe and splash damage, then it is useful to spam chain heal. Occasionally in raids I find the tank is taking too much damage, and chain heal can't keep him up. I have to use healing wave on him. It's a far superior single man heal.
Most of it comes from experience. It may take a while. Don't be discouraged. Eventually healing will come naturally. And if you run with the same tank alot as I do, you'll get accustomed to how they take damage. Though alot of that depends on the mobs they are fighting. As elemental damage messes my tank up faster than physical damage.
Learn not to use lesser healing wave. It's not like pallies flash of light. LHW is inneficient. If you can't keep the tank up with healing wave either the tank is very undergeared (or perhaps you are, and not right spec). Only times I ran into problems is with a duel wielding warrior "tank", another warrior trying to tank using a 2 hander, a 68 pally with 7600 health trying to tank BM, and a druid bear with only 12200 health trying to do heroic slabs. I'm to the point now I will inspect the tank, and dps before doing heroics and such. I refuse to run if I know we will wipe. I had a ret pally in my guild keep pushing for heroic SH runs, it isn't going to happen with that lack of dps (and I have seen his Kara numbers- they weren't great). If you lack too much dps, you will run out of mana healing.
Edited, Feb 13th 2008 9:38pm by thrashering