Some short things new people might want to know:

You need 1 account for each character you are gonna play at one time.
You generally need a software, i use keyclone but tried hotkeynet both are easy to setup and hotkeynet is free.
You can use any amount of computers, 1 computer to play 5 accounts or 5 computers or 3 or whatever number you want to use.
In some softwares you need to unbind w, a, s, d, q and e on other than main (different if you use more than 2 accounts but its the same thing, the basic thing in hotkeynet got this automaticly in itself so you dont need to unbind) so you dont move your other characters when you lead with your main but you should still have their movement binded on arrows or something like that.

Some macros:
follow
/follow Main_Character_Name

Use a ability
/assist Main_Character_Name
/cast Spell_Name

If you got more than 2 accounts you might want to use another way like for when the main dies
/focus Current_Window_Character --- one for each window and press it when you need to change main
and
/assist focus ---- think this should work, havent used it myself as i play 2 chars only
/cast Spell_Name

If you are gonna use a ability like silence, stun or such, in my way
char 1:
/cast Silence

char 2:
/assist Main_Character_Name
/castsequence ,,Silence ---- i keep more than 1 , becouse sometimes i press when abilitys is on gcd or is stunned, what it means with ,,Silence is that 3rd keypress will be silence, at first 2 nothing happens

Heal for 2 characters, just press without alt or ctrl = heal each others, alt = heal first, ctrl = heal 2nd.
I use so char 1 heal char 2 and char 2 heal char 1 with nomod becouse then if they kick or silence or stun or so they will most likely interupt the one who doesnt heal the character they dps.
acc 1
/cast [nomod, target=Character_Two_Name] Heal
/cast [mod:alt, target=Character_One_Name] Heal
/cast [mod:ctrl, target=Character_Two_Name] Heal

acc 2
/cast [nomod, target=Character_One_Name] Heal
/cast [mod:alt, target=Character_One_Name] Heal
/cast [mod:ctrl, target=Character_Two_Name] Heal


Other things you can write in macros between [ and ]:
exists - if the character is targettable pretty much
nodead - alive

These might be written different not sure
mounted
flyable - if you can use flying mount in that area


Think that is almost all information needed.