This spec is the basic and optimal PvE holy priest build:
http://db.vanillagaming.org/?talent#bxRhsV0oZdxtcc0VxThe 1 point in renew is the only point that you have some discretion with. When you hit 19 points in Holy, you have 1 point to put somewhere in renew, spell warding, blessed recovery, holy reach or searing light. You need to hit 20 points in order to unlock spiritual guidance. The only talent of those that will improve your ability to heal is renew, so why not put it in there to get 20 points.
This is the best build for pure PvE healing.
You may have people tell you that holy nova is useless for healing, and they are mostly right. The reason you take holy nova is because it allows you to aoe farm DM East. With the money you get there, you can buy your epic mount, enchants, gear, and most importantly, raid consumables. If you have another way to make a lot of gold, you can take the point from nova and put it somewhere else if you want.
Once you have a ton of gear (like 800 +healing), you can switch to a disc/holy build to get Power Infusion. I did so recently. There is a big debate about the precise best Power Infusion build, but this is the one I use:
http://db.vanillagaming.org/?talent#bxMusVVqobxtccAlso see this post for a nice visual explanation:
viewtopic.php?f=39&t=33731#p236801