Hi - I read through the forums here and copied the following macros. Before I do anything my first macro is:

/focus party1
/follow focus

then when I want to cast fireball :
/cast [target=focustarget, harm, nodead] fireball; [target=party1target, harm, nodead] fireball; fireball

and then for polymorph:
/cast [harm, nodead] Polymorph; [target=focustarget, harm, nodead] Polymorph; [target=party1target] Polymorph
/stopmacro [harm, nodead]
/assist focus
/stopmacro [harm, nodead]
/assist party1

which seems a bit long winded but works in a lot of situations. I'm not utilising the full benefit of this poly macro as I preset my poly targets by going to the mage screens and targeting them. Because my mages are going to fire on my focus' target they can sheep through the fight as they are sheeping their own target, it works really well.