One of the most potent ways we can speed up a heroic run is by using the right buffs for the job. I like to use Blessing of Might exclusively on any physical class, including the tanks. While you might think that Blessing of Kings would be better for a tank, the fact is that Might will increase their threat and DPS by a significant amount. Kings does provide extra life, but even if the tank was wearing greens, they'll usually have enough life for us to keep them afloat. I mean, we're holy paladins! You could let a warlock's imp pull all of heroic Pit of Saron and still keep the little demon alive if you point the Holy Light firehose at it. Let the tank know exactly what you're capable of, and give them permission to pull as many groups as you are comfortable healing through. Edit: some of the commenters have mentioned that your tank may be more comfortable with Kings instead of Might, so be sure to ask your tank which they would prefer before buffing.
Even if you're using a holy/retribution build, I suggest that every holy paladin use Righteous Fury in your heroic runs. If you're holy/prot, you end up taking less damage, and that's always a good thing. By generating extra threat via healing, you will also consolidate aggro from loose mobs onto yourself, which will make it easy for the tank to pick them up. That way, you don't have to be concerned with the rest of your group randomly gaining aggro on a surprise patrol. If you're keeping Beacon of Light on the tank, you can simply heal yourself to handle any incoming damage and keep the tank afloat as well. I haven't really found any mobs in Northrend heroics that interrupt casting, so you're typically safe with heal-tanking a mob or two. In addition, you should use Retribution Aura, as the extra reflected damage will outweigh the slight defensive benefits of any other aura.
The largest time sink in a heroic is sitting down to drink. With Divine Plea available once every 60 seconds and Seal of Wisdom active, you shouldn't have to drink at all. Use Divine Plea on cooldown, preferably when moving between groups of mobs, and use Seal of Wisdom to regenerate mana whenever you're not healing. If you're alert and use both of these powerful tools often, you'll find yourself never having to waste any Honeymint Tea. Keep your group moving as much as possible, and use our huge mana pools to handle anything unexpected.
I should also mention that Flash of Light can be your best friend in a heroic dungeon. It's cheap, fast, and even gives us a free HoT when cast on the tank. Considering that there is very rarely a huge influx of damage in a heroic, feel free to use Flash of Light to quickly top off party members and the tank and save yourself mana and time. Because it is typically only the tank taking any sort of serious damage, Glyph of Holy Light is rarely beneficial as well. I like to use Flash of Light primarily when healing the daily random heroic, augmented with the occasional Holy Light when we're fighting a hard-hitting boss. There aren't any 5-minute fights in a heroic dungeon, so feel free to even heal in excess if it keeps you moving quickly.
One of my favorite things about Icecrown are all of the undead enemies we face. We can use Exorcism and Holy Wrath in about half of the heroics to damage and stun our enemies, which can actually add up to quite a bit of damage when used often. I also use Consecrate, Shield of Righteousness, offensive Holy Shock, and Judgements to strike the elite mobs as much as I can. There is rarely a situation in which we must heal non-stop, so use those free GCDs to speed up the run a bit. On a particularly big pull, I'll even pop Avenging Wrath and my Talisman of Resurgence to maximize my holy damage and actually do reasonable DPS for a healer. Don't forget to use Hammer of Justice on cooldown as well, stunning a mob will not only reduce your incoming damage, but can be useful on enemies that like to run away.
The key to being effective in a heroic is to know what's coming, and be able to plan your actions accordingly. If there is a particularly non-threatening pull, you know you're free to unload all of your damaging attacks. When you know there's a boss coming up, you can refresh your Beacon and Sacred Shield spells on the tank so that you have more free GCDs to fight with. When facing mobs that root or slow your melee, you can use Hand of Freedom to let them get back to business sooner.
Our goal in a heroic dungeon is to use our entire toolbox to make the run as smooth and as fast as possible. There aren't too many people who enjoy running Azjol-Nerub for the 40th time, and so speeding up the tempo and keeping the run flowing will make it a more enjoyable experience for everyone. Use your superior HPS to handle any incoming damage, and then feel free to dish out as much of your own as you can. We weren't sent to Icecrown by Thrall and Varian to heal the Lich King's minions to death, so don't forget that a paladin is one part meditative cleric and two parts vengeful crusader.
The Light and How to Swing It (Holy Edition) is dedicated to helping holy paladins become the powerful healers that we're destined to be. If you're new to the paladin's healing ways, you can learn the ropes with our Holy 101 article. We also have information on how to keep a tank alive, how to heal a raid when necessary and how to beat the GCD. Tanking is a job, DPS is a craft -- but healing is truly an art.