I will try to explain my setup as clearly as possible, note this probably is not the easiest or most efficient method.
Here are screenshots from both my main and followers PvE. No fancy UI just basic wow in these pics.


The number 1 key on the tank is the old tried and true 9696, link here explains more.
That same link also has the click sequence I use for my shamans and many others! If you look at the action bar furthest east of the screen at the top are my 4 buttons referenced in my actual click macro. This button is also set to the number 1 key.

Key #1 tank 9696, shams dps /click macro
Key #2 both weapon buff
Key #3 tank does nothing, shams cast chain heal on each other
Key #4 tank 9696, shams flameshock
Key #5 tank conc shams thunderstorm
Key #6 + #7 situational for certain boss's, I switch macro's in and out here
Key #8 tank does nothing, shams cast water shield
Key #9 random things on both
Key #0 tank does nothing, shams cast grounding
Key #= is mount macro

I also have E set for 2 shams spamming lesser wave on tank, Q is spam lesser on self, P is drop totem farm and many other hotkey around my board.

While spamming the 1key I use my mouse to select certain skills that only require attention in specific cases, like pulling with avengers, buffs, trinks and bubbles. With this I NORMALLY just spam one key all day long and things die. Adapt to certain conditions and fights of course and try new things. With mixed teams it can become much more complicated but this has worked for me.