Proving Yourself: Endless Healer (Wave 30) (Level 90)

You see all those punk epeeners standing outside cities, with their full heroic gear, trying to act cool?

Well my friend, if you get this achievement, you can take pride in the fact that you have accomplished something just as hard as Heroic Raiding will ever be. And you can laugh in the face of the pathetic epeeners who think their gear makes them better than you.

You are the Proven Healer. You have mastered your role, be proud!

As a restoration shaman, I found it reasonably easy.

Learning the 10 waves is indeed the most important step to this achievement. Don't be intimidated by the 30 waves ahead of you. Once you can manage the first 10 waves, you will make rapid progress. It took me about 8 tries to work out how to handle things up to wave 11, and only 2 after that to get the achievement. But enough bragging, now for some real advice:

The talents are largely up to you to decide, except [spell=108282], which I highly recommend. When dealing with chomp-DoTs and ae-damage on the group, this talent is in my opinion the better choice over Rushing Streams. [spell=73920] will run up to 40 seconds, and usually the whole group except the hunter will stand in it, if you place it right (it's almost like a real group, but at least one range-dps is 'smart' enough to move up to the ae-heal). While HR is quite expensive, extending its duration makes it a very efficient group heal without interruption. In addition I also recommend the following glyphs: [spell=147781], [spell=55453]. I'll explain in a moment. I also added Healing Wave to my glyphs, but HST or Totemic Recall might be viable as well.

As for the tactics (in adddition to what is already mentioned in the excellent proving grounds guide):

Warrior, Rogue, Mage and Shaman (that's you), should stand in melee inside the Healing Rain. Always boost your HR with Unleash Weapon, the throughput is usually worth the GCD. At low damage you can use Lightning Bolt to keep the Rain AND Earth Shield up, while receiving a very slight mana gain and providing additional damage. And it will save you some ES-related GCDs.
Unsurprisingly you will mainly use Riptide (unglyphed for efficiency), Healing Wave, Greater Healing Wave and Healing Stream Totem as needed. Chain Heal can balance the group well, but suffers from its long cast time. Healing Surge should be avoided unless someone will die, but it will burn away your mana rapidly. Best learn to appraise when to let the HR do its work and when to heal directly.
As all shamans already know (hopefully), the class has loads of awesome cooldowns, which helps a lot in the fight. In waves 2, 5, 8 and 9 you can and will use your great healing CDs. In wave 2, 5 and 8 I dealt with a lot of damage on the group and used Healing Tide Totem, wave 9 will deal a lot of damage on the tank so [spell=73920] + [spell=114049] + [spell=98008] works great. Since each wave is 1 minute long, this combination will be available two more times, but make sure you have it ready for wave 9.
Besides interrupting enemies, your [spell=108269] will also come in very handy at least once per wave to stun all targets in melee and give you a valuable interruption from incoming damage.
And don't forget your early Mana Tide Totem: use it the first time you reach about 80% mana, usually during the 2nd or 3rd wave, then keep it on cooldown. The new Totemic Persistance talent will make handling (water-) totems a bit easier, especially when things get hectic, and they will get hectic.

I had success with my druid the following way:

I am going ahead and posting my cooldown list here, maybe someone will find it useful. A good advice is to try to "learn" the different waves, as it really helps to know what to expect.
I used Weak Auras to display the list on the screen so I could always have a look what was up next.

1 () - vigil
2 (AE) - tranquil
3 (2x Chomp) -
4 (2x Aqua) - kick / vigil
5 (AE) - tranquil
6 () - kick / vigil
7 (2x melee) - ironbark
8 (caster) - KICK / vigil
9 (AE) - tranquil
10 (melee) - kick / ironbark / vigil

For talents, there are some important choices:
Rank 2: Yseras Gift (Really important! Free smartheals without any mana-spending!)
Rank 3: Typhoon (THE gamewinner for you, if the nasty Flamecasters hit your party)
Rank 4: Force of Nature (Maybe also doable with [spell=114107], but the Trees are free and also smartheal!)
Rank 5: Bash (All mobs besides enraged melees can be bashed, it gives you a second to breathe sometimes)
Rank 6: Nature's Vigil (A little cleave-healing since the legendary won't work)

For gems: You can regem of course, but it is not really necessary. I went with my usual mastery-gems, but reforged to the first hastecap (3043). Do remember to have some spirit with you. I also used an int-flask with int-food.

Playstyle: Play VERY Mana-conserving! Never use Regrowth if you don't have the clearcast progg. You also need to cast [spell=5185] from time to time. Also, always heal off the "chomp"-debuff really quickly, even if it needs a Healing Touch. Frequently use the Trees, and make a little cooldown list if you have trouble timing them (see above for tips). The last tip I have for you is: Always (re-)plant the mushroom so your meeles, the meele-mage and yourself can stand in it, and use the [spell=56949] together with [spell=146654]! It really helps!