Well as a short story, i basically quit wow for a few months after my guild downed rag. i played a hunter, but recently got back into WoW playing my priest. I really love healing and have been casually healing 5 mans, but i want to start raiding on my priest as a healer. I haven't actually healed a raid group yet...or decided what spec i wanted to raid as. i like holy but disc seems pretty cool also, and most guilds (correct me if i'm wrong) tend to want a disc priest. so i don't mind going disc. the only problem is healing in a raid, i have yet to heal a raid group and was wondering how the transition from 5 to 10s and 25s mans would be. how can i become a great healer? any pointers or tips would be much appreciated. please respond and thanks for the input!!
O yes and one more thing...on my hunter i didn't use too many add-ons just the basics recount DBM and a couple others...so if you could recommend any add-ons for healing that would be awesome too!
I'm really not good at describing methods for healing, unfortunately. In raids, you'll find yourself spamming heals a lot more than in 5-mans, be it Greater Heal/Penance on a tank or PoH on the raid. I can toss out a few tips even if I'm not tremendously helpful - for PoH spam, you want to go group to group rather than spamming it on one group (if possible) because the HoT from the glyph overwrites itself. Prayer of Mending is a great spell to toss out wherever possible in a raid setting because there tends to be a lot more raid damage to bounce it than there is in 5-mans. Also, remember for Disc that Penance stacks up your Grace buff with each tick - if you have to switch targets, opening up with Penance is a great idea because it gets those stacks up quickly.
As far as Disc vs. Holy, it's the eternal debate. Disc is currently in a stronger position for serious raiding (better single-target healing, better cooldowns, and the shield mechanics are unique) but Holy still performs very well. Try them both out and see what you like.
For addons, I'd really recommend using a click-to-heal interface. VuhDo is what I use and love. You can set your mouse buttons, keyboard buttons (for example, pressing 1 while mousing over your heal frames will cast say Prayer of Mending or whatever), and ctrl+alt+shift modifiers for any of the above. It also can show you the Weakened Soul debuff and the remaining duration of Power Word: Shield, Renew, or Prayer of Mending on a person. Very handy.
The big advantage to this is you can target the boss while you're healing, which not only helps you see cast times or important buffs/debuffs on the boss/mob, but also helps a LOT with Smite (as Disc) or Shadowfiend.
Another very important one for Disc is an addon called Ingela's Rapture Timer. Very simple addon - it puts a moveable timer on your screen showing the time until your Rapture ability (the mana return from Power Word: Shield breaking) is available. It helps a lot with Disc mana management, you see the timer getting down to 1-2 seconds and you use PW:S on the tank to get another 7% back.
Vuhdo is very popular, and I personally recommend it as well.
As for disc vs. holy, remember in 4.3 that gap will be closed considerably with Holy getting a recovery CD in Divine Hymn. From what I've seen of the PTR, mitigation CD's haven't been as critical as they have been in H. Firelands. Hardmodes in Dragon Soul, which my schedule has prevented me from trying out, may change that however. If you do prefer holy, don't be afraid to make it your main spec.
My guild currently runs with a full time Disc, and myself has Holy/Disc. I highly recommend picking up both specs and playing around with them. When our full time disc can't make it I do stay holy for a few fights in firelands (Rhyolith, Shannox, and Rag).
I personally don't use healing addons and would say they are not required. With regard to advice about healing? Well.... heal like mana is going out of fashion whilst doing your best to keep it in fashion. Spec, gear and rotation with output and mana regen/regain in mind.
I play holy and Disc Atonement spec. If played correctly you will rarely run out of mana with either spec but both are great fun and desirable by most guilds. With both specs you will always be wanted.