I use a variation of this technique that works well for me in almost every situation.

My macro is:

/ac "Cure" <mo>
/ac "Cure" <focus>
/ac "Cure" <target>
/ac "Cure" <me>

I keep the main tank as focus target, allowing me to target the mob/boss. I mouseover the party window to heal other members, and if i want to heal outside the party (eg during a Fate) i can target them directly. I also dont have to keep setting focus target for each new encounter.

Its handy have the boss/mob targeted as I can see what the boss is casting, and if the tank loses aggro i can see who is about to need healing. I can also tab around if there are multiple mobs to keep an eye on them while never losing focus on the tank. I find I often lose targets in highly mobile fights (probably from rightclicking on the ground while moving, but this way i can always safely heal the tank just by making sure i'm not mousing over anything and casting my heals.