You are the Savior of the Weak and the Healer of Tanks. You, as a Holy Paladin, are the kind-hearted soul who strives so valiantly to keep the raid alive, even (or especially) if it's against other players.
Saving Their (Your Team's) Bacon
The healing profession, for any healer, has never been an easy rotation. You cannot just mash three or four buttons and then repeat. You have to react to who is being damaged right now. This means that you have to keep an eye on your team and must also have a good understanding of your spells and that you cannot rely on a 1 to 2 to 3 rotation.
Seal of Insight is your primary "Seal." It should be up at all times and it helps greatly with casting and mana efficiency.
Beacon of Light should always be active on a target, usually the tank. Any healing you do to the rest of the group will carry over, at least in part, to the target. This makes your job much easier.
Holy Power needs to be built up and then used on various abilities. Holy Shock allows us to build those charges of Holy Power and use them with Word of Glory and, on a critical strike/heal, grants us the Infusion of Light proc. Holy Shock should be used as often as possible to maximize Holy Power generation.
Note that a maximum of 5 Holy Power can be stored at any one time, though only 3 can be used. This allows us to pool some Holy Power for crucial moments where a quick succession of heals may be necessary. It also makes sure that we aren't wasting any HP points.
There's more, but this should give you a starting point.
Holy Stat Priorities
Like all spell casters and bolt lobbers the Holy Paladin's #1 stat is Intelligence. This stat increases the amount of healing done and even adds a bit of Crit Rating, which increases it even more.
Unlike melee types, ie: Retribution, Holy doesn't need Hit or Expertise for healing or much of anything. Heck, you even have an ability, Holy Insight, which Increases yourchance to hit with Holy Shock, Judgment, and Denounce by 15%. No added Hit is necessary.
Spirit, on the other hand, is the #2 "go to" stat. Holy Paladins use a lot of mana and can easily run out, which isn't a good place to be when fighting that boss or the players in that city your team is invading. It's necessary for you to stock up on Spirits (er... Spirit) to keep the mana level high enough to be effective.
Only after gathering enough Spirit to keep from bottoming out on mana should the Holy Pally look to other stats.
Haste becomes the next important stat. The upside of Haste is that it speeds up your casting times, speeds up your "Heal over Time" effects (HoTs,) and so on. The downside is that by speeding everything up you will burn mana faster. So don't go nuts with the Haste unless your mana is strong.
Mastery may be even more important that Haste. What it does is effectively increase your healing by placing a damage absorbtion shield on your target. Damage absorbed doesn't need to be healed and it doesn't increase your mana use.
Crit should be skipped. Yes, it makes for bigger heals, when the random numbers come up, but it's not reliable, where Haste and Mastery are.
Reforging is a way to push some of your stats around. Push your Crit and any Hit or Expertise into Spirit (if you need the mana.) Once you have enough Spirit then reforge into Haste or Mastery (pick one) and stack it up. At higher gear levels your Spirit should not be an issue.
Only use the other stat if that piece of gear already has the other, ie: if you're going for Haste the only reason to reforge to Mastery is if you already have Haste on that piece of gear and the other stat is something like Crit.
Gems and Enchants
This is really pretty easy. Have a gem slot that needs to be filled? Use the priorities above. Need more mana, stick in some kind of Spirit gem, otherwise use an Int gem or Int/Haste or Int/Spirit hybrid gem. Follow the same plan with your enchants. Spirit and Int first, and then Haste or Mastery.
Holy Talents, Batman!
Talents and glyphs are easily changed, whenever you need to change them. Just click on the new one, pay one "Tome of the Clear Mind" and you're good to go. Why change either? Because your play style and what you're doing (PvP, Raids, Dungeons, etc.) will vary.
Take these Talent recommendations and feel free to modify them as necessary.
As for the glyphs, there are a lot of them and some don't apply to you. Take a look at what you actually do and then if something about it bugs you see if there's a glyph to improve it. Buy them all, and by "all" I mean the important ones, and experiment with what works for you. You can
If you can't afford the gems and glyphs then you're going to have to spend some time earning some gold. The easiest way is to grab the Herbalism profession and then Mining as your second pick. Work them hard. Why Herbalism? Because when you have a high skill you get a massive Haste cooldown, and Haste is one of your best stats. (Both herbs and ores sell quite well.) Why not take skinning? Because you're Holy, and killing things isn't one of your better skills. ;) Otherwise, go for it.
It's time. The Raid needs you, again! Get to work!