For healing, your party/raid frames are critical. There are several different options you can use here.
Any of the options will require some playing around to set up. For this, I recommend using the proving grounds. Talk to a class trainer to enter, and it will put you in a scenario. You can use this scenario to safely mess with your UI and test it out with a group of NPCs. (Just talk to the NPC in the scenario to start the healing trial.)
Default UI
First, enter the proving grounds as mentioned above. (This way you can actually see and mess with the settings without needed to find a group.)
You will want to turn on raid-style party frames. In the interface menu, go to the “Raid Profiles” section. In the top right, make sure that “Use raid-style party frames” is checked. If you are in the proving grounds, you’ll now see the raid frames pop up. (Right now it will only have one frame — yours.)
You can get some basic options to adjust how these look in the Raid Profiles Interface screen. You can adjust the high and width of the frame, if you want to show mana bars, and such. A lot of this comes down to personal preference.
On the left side of your screen, you’ll see a grey bar, you can click it to expand it. The stuff we care about are the two bottom buttons, which affect the raid frames.
The “Hide/Show” button does what you would expect and hides the raid frames. Obviously, if you’re using the default frames, you want to show them. If you end up using 3rd party frames, you’ll want to hide these. (The 3rd party addon will probably do this for you, but it’s good to know where the option is.)
The “Unlock/Lock” can be used to adjust where the frames are. So, when you unlock the frames you’ll see a silver border around them. There’s a little tab at the top you can use to move them around your screen. The tab at the bottom can be used to resize the height (which will control when it starts a new column.)
The advantage of the default UI is that it’s easy to setup and maintain. If Blizzard adds some weird mechanic to a raid fight, the default frames will handle it on day one. The downside is that the simplicity means your options are limited for tracking stuff. So, the more stuff like hots healer has to track, the less useful the frames are. That means that resto druids are probably the worst off for using the default frames. Still, even if you go with an addon, I’d mess around a bit with the default frames to get a feel for them just in case you find yourself without addons at some point.
Addon Frames
There are lots of raid frame addons out there, and people tend to have their favorites. I’d probably recommend one that’s geared towards healers. The main ones would be Healbot, Grid, Grid2, and VuhDo. (Grid2 is not a new version of Grid, but a completely seperate addon with a different design philosophy. Grid is designed as modular, so you get extra addons to do more stuff with it, where Grid2 is designed as an all-in-one solution. Both have their advantages and disadvantages.) VuhDo and Healbot also use the more All-In-One approach. VuhDo (and I think Healbot) also have “click casting” build in, as an alternative to mouseover macros.
I’m not sure where the ElvUI raid frames fall on the spectrum of customization. (I’m sure it’s way ahead of the default frames, but not how it compares to the more traditionally healer focused options.)
Generally speaking, the more control they give you, the steeper the learning curve. If you’re planning to heal seriously at end game as a resto druid, it’s worth the time to learn one of them.