I'd recommend using uo assist for your targeting.
Older 2d targeting system
LastTarget
Newer more graphical targeting system
CurrentTarget
UOassist allows you another last target... which if you check the boxes on the first page for que targets and range check target will give you an added bonus.
The way I set my macros up are one macro per action.
Cast fireball = button 1
last target = button 2
UOA last target = button 3
heal = button 4
Here is a how to on how LastTarget works
http://oev.hilands.com/tips-targetingsystem.html