Mythic+

On mythic+ your focus is more on spot healing and burst. You forgo efficiency and long-term hps in favor of whatever keeps the targets alive through the most dangerous parts of encounters. Healing Wave gains a lot of value here being your main tool for spot healing and Healing Rain becomes your best way to keep Deluge active on targets after you consume your Riptides with Flow of the Tides

Where Does Your Healing Come From

Your major sources of healing are Healing Wave, Chain Heal, and Stormstream Totem. Unleash Life and Riptide serve as instant-cast spot healing tools and to improve the healing of your casted abilities. Riptide can also proc Stormstream Totem and Deeply Rooted Elements so it is very important that you keep casting it very often.

Healing Rain is an interesting ability in keys because the lower amount of players makes it harder to get full value out of it, however it is still worth casting and it is your best way to get full value out of Deluge and Flow of the Tides at the same time which is a very potent combo for aoe healing. You should aim to have it active as much as possible on a majority of the group.

Because so much of your healing is tied to your casted spells it is important that you actually cast them as much as possible. Downtime or having to move a lot drastically affects your healing and you need to be prepared for it by positioning properly ahead of time or using Spiritwalkers Grace efficiently.

Important Things to Know

• Stormstream Totem is a very good tool and you can stack multiple of them. Keep using Ancestral Swiftness on cooldown but save the Stormstream Totem if it isn't needed at that moment, you can have up to two charges stored at the same time. When heavy damage happens you can drop your two banked Stormstreams and even drop a third if Ancestral Swiftness is again back off cooldown. This is a great way to have another small healing cooldown.
• Healing Rain is valuable even if you don't get a ton of healing from the rain itself, but it can also become not worth using if you are in a group full of ranged players and simply can't get more than two players into it.
• Healing Stream Totem is good but not incredibly, if you have to stop using it for some period of time in order to save Stormstream Totems then that is perfectly fine but otherwise try to use it often. It can be good to drop two of them ahead of damage or while moving when you don't have a lot of other valuable casts anyway
• During Ascendance Chain Heal becomes much stronger because the reduction from target to target is much smaller. You won't get benefit from the extra targets because players can't get healed by multiple jumps of the same cast but the spell still heals for a lot more.

Gameplay

You will use your short cooldowns as much as possible and try to keep Riptide coverage in the group, to deal with heavy damage you use Healing Wave or Chain Heal depending on how many targets need healing and how urgently. Aim to cast Chain Heal into the players whose Riptide will expire sooner to minimize the healing lost from it

1. Use your Stormstream Totems smartly. Cast them as soon as you get them if healing is needed or save them for later if not. You can bank up to two charges of the buff and have Ancestral Swiftness ready again for a third if you set it up properly.
2. Cast Riptide. Even if no one needs healing at that moment it can be a good idea to use it on people to avoid capping charges, every cast has a chance to give you a Stormstream Totem or activate Ascendance and having the buffs lets you start healing faster with Deluge and Flow of the Tides.
3. Use Ancestral Swiftness on cooldown. This is your Stormstream Totem generator and you should keep it on cooldown as much as possible, remember that you can save the procs for later if they aren't needed at the moment you press the spell.
4. Cast Unleash Life on cooldown. This is a spot-healing tool, an ancestor generator, and a buff to your follow up casts. Just an all around good value spell to use.
5. Keep Healing Rain active under as many players as possible. In most groups you should be able to have three or more players in it which makes it worth using, if the group is heavy on ranged you could look into dropping the spell but the ideal scenario is that even ranged dps come close together to make them easier to heal. Even outside of rain things like the max jump range of Chain Heal can make it hard to keep the group alive if people aren't somewhat close to each other.
6. Use Healing Stream Totems often, cast two of them together if any healing is needed and you have them. This is a bit of passive trickle healing that can help you keep people topped but won't do a lot on its own. The spell is worth casting but also not super high priority, which makes it find to hold on to them if you are trying to line up Stormstream Totem with damage events.
7. Use your filler spells. Your main source of direct healing is gonna be Chain Heal and Healing Wave so after all the other cooldowns that increase the effectiveness of these are taken care of you spam the correct spell for the current situation as much as possible. Chain Heal is your tool for aoe healing and you want to aim towards players with Riptide to use Flow of the Tides while Healing Wave is gonna be your spot-healing tool.

During Ascendance the same conditions apply for picking between your filler spells, however they become so strong that you opt into casting them over and over again and can drop down the priority of other spells. Ancestral Swiftness is a special case because it doesn't incur a global cooldown so you should still use it as soon as its up, but it is not uncommon to find yourself ignoring other spells for the duration of the buff. Pairing Ascendance with Spiritwalkers Grace is a very good option and can be very important to make sure you get value out of it no matter what.

Conclusions

A decent amount of your casts are gonna be spells that, while good on their own, mostly enhance the strength of your filler casts. Those are the meat of your healing. You should keep the cooldowns flowing because they are very efficient, and mean you are always prepared to respond to damage when it happens, but the casts that are gonna move health bars and keep people alive are very likely to be Chain Heal and Healing Wave so they deserve your focus.

Restoration Shaman is a very good mythic plus spec with a kit that can respond to most situations, on the surface its a very simple spec that simply casts to heal but deep down it can have some intricacies that reward planning and proper usage of resources. Learn what those are and how to maximize their value and you will be able to do any content the game throws at you.