Everyone has their own style of (I will pick healing for this discussion). Things for my and my playstyle.
I don't like targeting anything, almost ever. So I put targets in my options for spells:
/cast [@focus-target, help] HealSpell
/cast [@focus-target-target] HealSpell

I don't like to figure out who is getting hurt. It is probably since I love pet classes and I like them to share the damage. I leave all their growl/aggro abilities on and they swap out tanking 90% of the time. So they all get hurt, but they all don't get hurt as bad. But that means 5 chars and 5 pets to worry about and figuring out who's pet has aggro and is getting beat down. I just let the mob decide who I am going to heal. So I heal whoever the main's mob is targeting. [@focus-target-target]

I also like to heal in BGs a lot. But they aren't in my party and sometimes, they aren't even in my raid (WG) (or out in the wild while leveling). So I add in a way for my main to pick a target to heal specifically. 9 times out of 10, you can still just heal whoever is getting beaten on, but sometimes, 2 people might get beat up and you need to heal a person without figuring who is attacking. So: [@focus-target, help] covers that.

But in a WG or AV swarm (30-60 people), it is hard to pick out who exactly is getting hurt. " V " isn't very good since there are way too many of them, so I still like the heal whoever is getting beaten on. Tab target an enemy and heal the person he is trying to kill. No thinking, no wondering just heal: [@target-target] HealSpell for my main and [@focus-target-target] HealSpell for my alts.

Other people use heals for each specific char, but that is hard if you have more then 5 (pets). That seems hard to do with BGs or WG. Unless you just don't heal others, which seems selfish. That takes a lot of keybinds and even though I have a Logitech G15, I still don't like to use too many keybinds. I pretty much just use 1 button to heal. I just put all 2-3 casts in the same macro and let the system figure it out what to do.

Other people use click/mouse regions to heal. Not so bad, but I don't like using my mouse more than I have to. I don't like relying on addons to do actions. What if the addons break, I have to either stop playing or do it another way until they come back. Macros in game pretty much can't break and have no downtime. Then there is my own paranoia that what if they outlaw mouse broadcasting. I like using it, but I don't rely on it. With ,,,,,,, in sequences going away, they are allowed to change anything at anytime.

The next part is just how to do step up amount of healing. You can put in a specific class on your own. The basic idea is when I am out questing, I don't need much healing, but every once in a while, I want more. Then when I do instances, I want even more. So I put in small heals and a reset on a castsequence so I can step in heals.
/castsequence [@options] reset=8 TinyHeal, SmallHeal, BigHeal, OMGHeal
You can even spread out heals across chars. Say your shammys use lesser healing wave, but it is too small, you can have 2 of them heal at a time to make the heals bigger. Say your pallies flash heal is way too small, you can use 2 and then 3 of them at a time to make heals bigger. Maybe you want 1 to heal first, then 2, then 3 to scale up how much heals with a quick small spell to spread out the mana used.
(char1) /castsequence [@options] reset=6 LHW, , LHW
(char2) /castsequence [@options] reset=6 , LHW,
(char3) /castsequence [@options] reset=6 , , LHW
(char4) /castsequence [@options] reset=6 , , LHW
etc.

Lots of different ways to do things. Maybe just pick one that works with your playstyle.
Hope that helps and good luck.