Don't heal. Easiest step of all. Throw in DPS spells. Heck, if you have the ability to taunt the boss, do that as well. Play a different role other than what you were originally asked to do for a specific encounter. It'll be a surprise that the rest of the raid can look forward to. Keep your DoTs up, right?
Don't stay focused. Too busy playing Bejeweled on my iPhone, and I just hit 500k points -- can't pay attention. Hold on, let me build one more farm in CityVille. One sec, guys, I'm being attacked by a Baneslayer Angel in Magic: The Gathering! Let me cast Path to Exile first! While you're at it, can you keep the volume down some? I'm trying to catch up on some Community on TV here!
Consistently obsess over meters. Whether it's farm content, progression content or PvP, you should always bury your face in different healing meters. For bonus points, call the healers who do better than you try-hards and make fun of anyone else below you. Berate them and do your best to get under their skin until you're at the point where no one wants to bring you to their raids anymore because you have alienated the whole server.
Do not use your raid cooldowns. What possible difference can these 3-minute-long cooldown spells make, anyway? They only last for a few seconds, and they hardly make an impact in the grand scheme of things. You're good enough that you don't even need to rely on those abilities at any point.
Conserve your mana like crazy. Mana is like money in stocks -- the more you have, the larger the interest. Surely that mana pool is going to get larger and larger. You should be spending as little mana as possible. Rely on the other healers to do the job and get them to burn their mana instead of you. Be the guy who rides the three-seater bicycle in the back seat who doesn't pedal!
Heal just yourself. Isn't this every player for himself? All the other players have their own forms of protection abilities and self-heals. That's what bandages are for. The performance of the other players is of little concern to you. You're the most important player in the raid!
Don't worry about mana regeneration. Feel free to completely tank your mana to the point of oblivion. Even when there's still a boss standing in front of you who is using abilities that your raid manages to somehow dodge, you should still land spells unnecessarily and constantly. Forget using the different abilities you have to get mana back. They're all pointless.
Stand in everything bad. You have healing spells -- you can handle standing in all the various void zones and fires, right? Don't listen to the other raging idiots around you yelling at you to get out of that bad stuff. Don't they know who you are and what you are capable as a healer?
Heal the wrong assignments. Pick a player and go to town unloading every drop of healing spell you have. Don't follow the instructions your leaders laid out for you. What do they possibly know about healing or what the objectives in a boss fight are?
Don't do any research on your class. Use whatever spells you like. You can throw this whole efficiency business out the window. Heal whoever you want. Heal however many people as you want, regardless of what their health is. Use fast heals when the rest of your raid isn't under the imminent threat of death. Use slow heals when players are taking damage too quickly. You can tell your raid that you tried.
Don't ever buy consumables. Flasks? You don't need that stuff. Potions? Waste of gold. You shouldn't have to rely on external substances to enhance your performance in the real world. So why should you in the virtual world?
Don't ever buy enchants or gems. Augments aren't that big of a deal. You don't need the fancy leg patches or a shoulder or head enchant. They don't give that much of a boost to your stats, anyway.
The road to ruin
There are other methods on the road to becoming the worst healer on the planet. I'm sure you can come up with more ideas. Or maybe you've seen some great examples in your history of raiding.
But in all due seriousness, don't do any of these -- at least, don't do them unless you have a solid reason as to why, and it ends up being contextually relevant. While you can ultimately come up with exceptions for almost all of the above points, it takes a disciplined and skilled healer to know how and when to do it.
The worst healers are the ones who do something without truly understanding why they're doing it in the first place.
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.