Ok. This is a thread that will be referencing Jynus's resto guide a bit, so please if you haven't read it you should. Its stickied at the top of the US official shaman forum. Amazing guide, thank you for all the help you've given shaman throughout the game with it, and me included.
I admit first off that I don't have the time to crunch numbers, I am a casual player for the most part. But I did take the time to learn what I am doing and how to heal under the new model. There is one thing that really bugs me on these forums as of late: its resto shaman complaining constantly about how healing is broken and that they can't heal anything. Every single one of them is either geared wrong, stacking the wrong stats, or not taking advantage of enchanting, reforging, or even gemming their gear with anything (seriously, if you're poor in game grab a wrath epic gem. They cost like 20g).
I personally find myself to be a much greater healer since I stack mastery. Yes, this style of healing requires letting people's health drop somewhat below max before you start healing them, that's what Cata has allowed us to do. I almost never oom in a heroic these days, even if the dps stands in the fire or if aggro somehow gets messed up. I personally think every one of you shaman that are having issues should go for the following stat arrangement:
916 haste (I admit I go a little over, that's ok. about 1K haste max I'd say)
2K spirit (go over if you can, and don't reforge off spirit from your gear. It really does make a difference especially with mana tide totem.)
1K mastery (this is a minimum, go as high as you can get, once you change over how you heal you'll find this to be the single most effective stat you can use as a resto shammy)
Other stats that we should want as well are:
INT (obviously, the more we have the more spellpower and mana we have. I recommend no less than 80K mana for heroics and current raid content. Again, more is better as long as you don't slack in other areas)
CRIT (this will come passively, and I highly recommend speccing into the 3% crit from elemental tier 1. I actually reforge off a lot of crit. I think this is the most effective way to get your mastery up as I still crit more than enough to take advantage of the 10% damage reduction when I need it)
Now for rotation: I try to make sure a riptide is out and then pop 2 healing surges while I have tidal waves. I don't worry about topping anyone off except after a pull is over. Now if you have nothing else to do and want to top people off anyway, use healing wave. Its cheap (in fact my mana regen compensates for me to spam it), and will allow you to top people off if there is no incoming damage.
I also use my healing stream totem over mana spring now. It took me a while to realize this, but the healing stream's free heal to everyone really does outweigh the extra 300 something MP5 that you usually get from a pally or a second shaman anyway when you're in a raid. And since we no longer have a talent that improves mana spring totem there is no reason any resto shaman should be using it once they reach the stats I mentioned above. Healing rain, greater healing wave, and chain heal all have their situational uses, and you will use them quite frequently (especially healing rain).
I find healing rain to be the most effective group heal we have. If needed I throw down a healing rain and then will throw out a couple of chain heals to help with that. It works great in the right situation.
Next is greater healing wave. This spell I primarily use with Unleash Elements to make it even larger. I also try to save Nature's Swiftness for it if the tank is extremely low. Sometimes I'll use Nature's Swiftness for a healing rain if a lot of aoe damage is going out (spike aoe I think is the right term), but usually I save it for a Greater Healing Wave to go on the tank in an emergency. The only times I ever throw a GHW on any dps is when I know the tank is safe and the dps is hovering at less than 30% health without taking any or much incoming damage.
After you practice this for a while you'll start coming up with your own strategies and tips. Always think while you're healing about what you're doing, don't let yourself get distracted by the tv or whatever else might be around you. This will cause you to be inefficient and go oom too quickly.
One quick final tip: If you find yourself starting to go under 50% mana and there isn't much incoming damage: stand there and let people get to around 50% life before throwing heals out again. Especially while you stack mastery this will prevent you from ooming in most situations. Now dps still has to move out of the fire and tanks still need to use defensive CDs when the time is right, so if a group wipes its not always on the healer now. But seriously, I find myself being able to prevent groups from wiping to some mistakes. Now repeated mistakes in the same encounter will still spell a wipe, but 1 or 3 mistakes are ok with me now.
Combine this with Jynus's guide and you shouldn't have any issues healing as a shaman at all. If you need some extra advice please feel free to post here or contact me in game. Thank you for your time. I hope you find my advice useful.