Set-Up (Part 2):
In part 1, we have each toon able to become the leader of the group.
When they do so, they switch to Action Bar 2.
All of the other toons promote that toon to Party Leader, and switch to Action Bar 1.

Initially, on logging into the game, all toons will be on Action Bar 1.
So, you'll want to press the switch leaders key, even if you're already on the correct leader.

There will be two general types of macro's we'll use here.
The first type is an assist macro. The second type is a round-robin macro.
The majority of our spells will use the first macro type.

The reason for setting up Paging action bars in Part 1, is because we use this syntax for assist:
/assist [target=party1]...... or..... /cast [target=party1target]......

Within Warcraft, Party 1 is the party leader, if you're not the leader.
If you are the leader, it is the party member who's name is directly beneath yours.
The command "/target Party1" has the same effect as pressing F2 in the default keybindings.

With our assist syntax, each non-leader would assist the leader as desired.
However, since we do not want the leader to assist a slave (their party1), we need them on a different Action Bar.

Going with an example of Shaman's, who are the most common boxing team...
To switch action bars within game, press Shift 1 (for action bar 1) or Shift 2 (for action bar 2).

When the toon is the party leader, they'll be on action bar 2.
Each toon will have Lightning Bolt on keybind 1, on their 2nd action bar.
If your toons are mages, you might choose Fireball as your main spell, instead of Lightning Bolt.

When the toon is a slave, they'll be on action bar 1.
Every toon will have a Lightning Bolt assist macro, also on keybind 1, but on action bar 1.
For these macro's, I like to pick the red question mark as the icon, so whatever spell I'm casting will be the icon displayed on my action bar.
I like to have these macro's on the character specific tab, as other toons on that account won't need these exact macro's.

I recommend prefacing either #show or #showtooltip, prior to the active macro commands.
With #show, you will see the icon of the spell.
With #showtooltip, in addition to the icon, you can mouse-over the icon for the in-game tooltip.

The master (Action Bar 2) spell will be a Lightning Bolt dragged from the (P) spell book.
No macro is necessary for the party leader. We can get fancy and add macro's here down the road, if desired.

Each slave (Action Bar 1) will have a macro for Lightning Bolt in this same slot.
Their macro will either be Macro A or Macro B.
In Macro A, the slave will display the masters target as they attack it.
In Macro B, the slave will not display the masters target, but will nonetheless attack the master's target.
Macro A is generally better for PvE, as you know exactly what your toons will attack.
Macro B is very strong for PvP, as you can have all your toons attack the priest, while they all target the rogue.

Macro A
Line 1: #show
Line 2: /assist [target=party1]
Line 3: /cast Lightning Bolt

Macro B
Line 1: #show
Line 2: /cast [target=party1target] Lightning Bolt

We can repeat this for most other macro's.
Even other macro types. For example:

Master on Action Bar 2:
Line 1: #showtooltip
Line 2: /cast [nomod] Lava Burst
Line 3: /cast [mod] Flame Shock

Slaves on Action Bar 1:
Line 1: #showtooltip
Line 2: /cast [nomod, target=party1target] Lava Burst
Line 3: /cast [mod, target=party1target] Flame Shock

With these macro's, the party leader and slaves Flame Shock if the key is pressed with Alt, Control or Shift.
If the macro is pressed without a modifier key, it is Lava Burst, all of them on the Party Leader's target.

We can get creative with heal type spells too.

Master on Action Bar 2:
Line 1: #showtooltip
Line 2: /cast [help] Gift of the Naaru; [help, target=targettarget] Gift of the Naaru; [target=player] Gift of the Naaru

The Slaves on Action Bar 1:
Line 1: #show
Line 2: /assist [target=party1]
Line 3: /cast [help] Gift of the Naaru; [help, target=targettarget] Gift of the Naaru; [target=player] Gift of the Naaru

This macro has multiple targeting parameters. It will cast on the first that is true.
It initially checks if the target is friendly. The slaves assist the master. If the master's target is friendly, they all cast on it.
If the master's target is hostile, the first condition fails and the macro attempts the second condition.

The second condition, is if the target of the target is friendly. When you attack a mob, it will attack one of your shaman's.
The mob is hostile, but your shamans are friendly, so the heal goes to the shaman the mob is attacking.

If you're targeting an opposite faction toon, who is also targeting an opposite faction toon, the first two conditions fail.
Which means the last condition [target=palyer] has each shaman target themselves for the Heal Over Time.

You can combine this type of heal very easily with all of your heal spells.
If you go with either a mixed team, or a dedicated healer, the healer can use this to great effect.
They cast on friendlies by having the party leader target a friendly, and you click their heal macro.
During combat, the same macro has the heal go to whoever the hostile mob is attacking.
If your mixed team consists of Tank + Healer + 3x DPS, the healer will heal the tank, as long as they hold threat.

Going with a Druid example, combining Hot Keys via macro's.

Master on Action Bar 2:
Line 1: #showtooltip Wrath
Line 2: /cast [help] Rejuvenation; [harm] Wrath

Slaves on Action Bar 1:
Line 1: #show Wrath
Line 2: /cast [help, target=party1target] Rejuvenation; [harm, target=party1target] Wrath

With these macro's, if the target is friendly, a Rejuvenation is cast.
If the target is hostile a Wrath is cast.
On the slaves, the Icon of Wrath is always shown, with no mouse-over tooltip.
On the master, the Wrath icon is always shown, with the tooltip also shown if you mouse-over the macro.

Another type of macro is the round-robin.
This will generally be macro's which do not rely upon assist or targeting.

With shaman's, in addition to having each drop specific totems at once, you'll frequently start a fight and a default set out.
Each will have the same Line 1, but Line 2 will vary by shaman.
Assuming the classic 4x Shaman + 1x Paladin; one of the shammies could be Resto Spec.

Line 1: #show
Line 2: Each Shaman will have their own line here.

A: /castsequence reset=8 Totem of Wrath, Healing Stream Totem, Grounding Totem, Stoneclaw Totem
B: /castsequence reset=8 Grounding Totem, Healing Stream Totem, Strength of Earth Totem, Searing Totem
C: /castsequence reset=8 Cleansing Totem, Grounding Totem, Stoneskin Totem, Searing Totem
D: /castsequence reset=8 Mana Spring Totem, Grounding Totem, Tremor Totem, Searing Totem

I generally like Searing/Magma totems towards the end of the Totem Farm macro.
Mainly because they can pull, which I might not want as I'm dropping totems.
Also, more important totems are dropped first, less important are dropped last.
Generally, if I have a Resto Shaman, they will drop the Mana Spring since that won't stack with other Mana Springs, and occasionally they'll go Mana Tide instead.
Resistance totems are not included in this Totem Stomp macro, but they're easily inserted.
The reset=8 means, if 8 seconds pass without pressing this macro at all, it resets the sequence.

Valid arguements for reset include reset=target, reset=combat, reset=shift, reset=8.
In the case of Target, it resets when a new target is chosen. Could be useful for warlocks with a dot sequence.
Reset=Combat, resets when combat ends.
Reset=Shift resets when shift is pressed in conjunction with the macro.
Reset=8 (or any other number you choose) resets after that many seconds of not pressing the macro.
As always, when you run out of spells, a sequence will loop to the first in its sequence.

You can use similar cast sequence for Fire nova, Earthbind, Thunderstorm, Tranquility, Polymorph etc.

Shaman 1
#showtooltip Thunderstorm
/cast [mod] Elemental Mastery
/stopcasting
/cast [mod] Thunderstorm
/castsequence [nomod] reset=45 Thunderstorm,,,

Shaman 4
#showtooltip Thunderstorm
/cast [mod] Elemental Mastery
/stopcasting
/cast [mod] Thunderstorm
/castsequence [nomod] reset=45 ,,,Thunderstorm

In this case, the key can be pressed in sequence for control, with each shaman casting it after the other.
Alternatively any mod key will have all shaman's cast Elemental Mastery and then Thunderstorm for a possible Nova burst.
Talented, Fire Nova stuns and Earthbind roots, so these are candidates for a castsequence.

In a Paladin x1 and Shaman x4 (3x Elemental, 1x Resto), you might find a macro like this:

Paladin
Line 1: #showtooltip
Line 2: /cast [mounted] !Crusader Aura; [nomounted] !Concentration Aura

Elemental Shaman's
No macro, Water Shield straight from the ability book.

Resto Shaman
Line 1: #show
Line 2: /cast [mod:alt, target=party1target] Earth Shield
Line 3: /cast [nomod] Water Shield

With this, on a single keybind:
The Paladin will Crusader Aura once if mounted. Pressing it again will not turn the aura off.
The Paladin will Concentration Aura once if not mounted. Pressing it again will not turn off the aura.
The Elemental Shaman's will refresh their Water Shield.
The Resto Shaman will refresh their Water Shield, or Earth Shield the leader's (probably Paladin Tank) target, if pressed with a modifier like Shift, Alt, Control.