Typically, linking your armory is a good place to start. I know little about healadins other than I like it when they are healing me but most of the healadins I see sport +int gems instead of SP or SP/Intellect hybrids for their metas.
There are two different styles of Paladin Healing - Flash of Light spec, which focuses around Flash of Light, and Holy Light spec, which... well you know.
Flash of Light spec is good at pumping out small, mana-efficient heals for lengthy periods of time. This is a good idea for 5-mans or even some 10-mans, but many feel that it is inadequate to heal serious content. It's more of a raid-healing spec than a tank-healing spec - think of yourself as a living HoT. Sometimes it works, but typically endgame Holy Paladins are HL specced.
FoL would gem pure spellpower, because it is so mana-efficient and spellpower helps offset the weakness of FoL itself.
Holy Light spec pumps out the big, expensive Holy Light bombs. Beacon one tank, bomb the crap out of the other, keep them both alive. This is what the vast majority of Holy Paladins do, especially in endgame or hardmode content.
HL gems pure int. Spellpower is mostly overheals in this scenario, and Holy Light just costs so much mana that you need every spare ounce of mana regen you can get. Besides, it gives you a small amount of spellpower too.