I don't use macro's much, or addons for that matter...So I can't really help with that. I just have my spells on the default UI bars, with some of my toggle ones being on the upper bar so I can easily click on them while using the 123 bar to cast spells.
As for healing in dungeons, it's really not that different from dps or tanking in that you have your targets, and you have you'r spells and it's just making sure you cast the right spell on the right target. Healers have it even easier because they have the same targets all the time.
Shield and renew were my most cast spells in dungeons while leveling. Icy-vein's has this
handy guide.

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