One does not simply walk into Firelands without the best gear available. If you're rocking mostly gear from Firelands normal mode along with a few items from the daily quest area vendors, then yes, you are prepared.
Don't think you can walk into heroics with an alt that you're just dusting off after being bored by things to do on your main. You should be at the point that there is nothing left from the valor vendor for you to purchase. Ideally, your character would be at a level that no longer needs additional gear from normal Firelands, crafted recipes or vendors. But you can probably get away with a little less than that.
Boss order of operations
This one is entirely up to your leaders. I'd highly recommend Shannox as a good opener. Not only is it one of the easier opening hard mode bosses to work on, the boss also drops heroic leg tokens. He's also a great skill check for both the players and the raid as a whole.
After that, the strength of your guild should dictate boss your group should pursue. If they're excellent at mobility and awareness, then take a crack at Alysrazor. One of the extra changes is that there are meteors that come falling out of the sky that players need to hide behind.
Expect to do more with less
If your raid has high DPS, then opt for Beth'tilac or Lord Rhyolith. Be advised that those fights have fairly high DPS requirements with the additional mobs and such that your group needs to deal with. Your raid leader may drop a healer from the composition to try to bridge that DPS gap. Be prepared to stand on your head and five-heal it. If you're on 10-man, I'm not sure if dropping a healer is even possible, even after the nerfs.
Attitude is extremely important going into the heroic mode stuff. Hard mode is going to be hard. Don't expect to push through and expect the bosses to topple over after a few shots. Those expectations are absurd. By all means, aim for them, but just don't be disappointed. I've been on unfortunate raid nights where the atmosphere plummeted after only a scant few attempts on certain hard mode bosses, where everyone expected each other to play flawlessly on every attempt. With new mechanics, there is a new learning curve that needs to be respected. It'll take time for some players to catch on to it.
Expect some stronger than usual flak from your leaders or from other players. Every healer has undergone some sort of criticism before in the past. Remember to stay calm about it, and don't lash back. Keep your logs, parses and other combat recording addons ready to prove what the facts of the wipe are. Don't assign blame just yet. Focus on what happened and what can be done to avoid the situation from occurring again. Above all else, do not let the negative players get to you. It'll only disrupt your focus even further and cripple your ability to play at the level you need to be.
At the same time, any simple or sloppy mistakes made on normal mode content cannot be so easily looked over or forgiven on heroic. Expect errors to be punished severely (to the point of a wipe). Drill that point home to your healers, at least. They have to bring the best possible game.
Be as objective as possible when giving feedback to other healers. Ask questions about what they're doing and what they're noticing. Figure out if they're struggling anywhere and don't hesitate to move people around to shake things up to see if that resolves any of the issues. Some healers just have a hard time trying to do things on an encounter that they're not used to.
Instead of looking at a specific parse or two, try to identify trends. Every player has the one attempt where they just goof up on something that should've been easily avoidable or foreseeable. Try to maintain a list of anything notable. For example, if the same tank continues to die four attempts in a row, it may be time to change healers, add another healer or switch tanking assignments. While it is possible that the tank could simply be a bad player, I doubt the player will make it far in heroic Firelands anyway.
Doublecheck your consumables, buffs and character
It may have been possible to get through normal mode with little or no consumables (potions, flasks and food), those items will make a larger difference on heroic. You'll want every possible advantage you can get. If you have a nasty habit of forgetting to click on buff food or using your flasks, then you should put them on your bar somewhere or set a reminder for yourself. You're going to need all of it.
Check out your character's talents and glyphs. Instead of using cookie-cutter builds and recommendations, take a moment and think about the merits of your points and glyphs. Each point matters. Make it count. If you're not going to be doing any Smiting, then you may not want to take points in Archangel (as an example).
Good luck with your efforts in Firelands! Any of you veteran healers who have already cleared your way through parts of the hard mode version of the instance have any advice for players just getting started?
Need advice on working with the healers in your guild? Raid Rx has you covered. Send your questions about raid healing to firstname.lastname@example.org. For less healer-centric raiding advice, visit Ready Check for advanced tactics and advice for the endgame raider.