I'm not sure of a guide but mine is level 20 so I can give you a few pointers.
First I find that RP not a very offensive class so I leveled mine solely on RvR. This has worked out well because I am usually on of the top on the EXP due to the fact that I don't die often and each person you heal that kills someone you get part of the exp.
Healing
The first thing I do in a scenario is bring up all parties so I can see them. This can be done by clicking the check box at the top of the party list. As we are running into combat I put my HoT(Rune Of Regeneration) on all tanks and front line DPS. You know they are going to be taking damage as soon as the clash occurs so you might as well have the heals already ticking. After tanks and front line DPS I drop HoTs on BWs. They are going to be exploding so might as well keep them up and doing damage.
At this time, I do a quick evaluation of everyone's health. If everyone is near full, I will finish HoTing up the rest of my team and the other team (Don't forget yourself). Usually by this time people are starting to get hurt or one or two tanks are taking heavy damage. I start off by casting Rune Of Mending and follow it with Rune Of Regeneration. If you hit your HoT right before Mending is done both spells will go off at the same time. If their is a second tank I'll hit them with the same combo.
If this happens to be a squishy class or a tank that is taking substantial damage and I'm trying to save them I will follow this combo with a Rune of Shielding and start immediately casting Rune Of Restoration. The shielding will by you a bit of time to let the dots tick and for you to get off your Rune of Resto.
If the tanks are only taking moderate damage and the Rune of Regen/Mending will take care of them I cast a Rune of Serenity next on the tank. This heal will be a third hot on that tank and will bounce to the next tank or melee DPS in area and heal as it goes.
Once I'm sure the front line tanks are good and no one is about to die anytime soon I begin my HoT rotation again.
Choosing Who Will Die
Inevitably you will come to a point in your healing career that you will have to make a decision on whether to let someone live or die. In heavy battles you will not be able to keep everyone alive as your AP will soon be depleted and your next heal will rely on the next tick. Making the right decision in these circumstances can make the difference between win or lose.
There are those that would like to say this is as easy and list an order of say tanks, healers, RDPS, MDPS. I disagree. Every class is needed for a successful victory and if all your MDPS and RDPS is dead you will soon find yourself dead after they burn down your few remaining tanks. There will also be those DPS character you will notice that will be more prone to killing themselves by charging the group or are just low in levels.
That being said if the fight is heavy I'll generally try to keep other healers alive first. Tanks generally second if they are not low level and dieing fast. Then DPS. Often times I will still throw a single hot on a DPS and let them try to survive with their on survival tactics. Often this is enough to keep them alive long enough that when the pressure stops then you can bring everyone back to full.
If at all possible, at least throw a HoT on a character you know is going down. If by chance they break free, the HoT may keep them alive and at least they can't complain they didn't get a heal.
Rezing
Rezing in combat is very situational. It is better to keep everyone alive than to rez someone. I only rez when the rest of my team is near full and I know I have HoTs on my key players. The only exception is rezing a healer. I will rez a healer and take the chance of losing any other class even a tank. Once the healer is up and back healing. I will make every effort to rez the person I lost while I was rezzing the healer. This may not be immediately as I might have to get heals off but I will make an attempt.
Surviving
Watching the flow of battle is paramount to a healer staying alive. If you are on the offensive, moving with your lead attackers will help you win. The front advancing line won't survive long without heals and others (especially those that guard healers) will realize as you move up that they should too.
The same goes for when you are being ran over. Pulling backing and surviving means your able to keep healing your team. Don't forget to HoT as you retreat. Keep it up on those retreating with you so they can stay alive from the onslaught of instant cast damage they are going to take as they run. These people will be your new wall wherever you stop the retreat. Remember also that as a RP you have your instant heal (Grungni's Gift) that you can spam on the run. It might not heal for much but with your HoT it might keep you or someone else alive.
When you get jumped by a WE or Maurader, the first thing you should do is hit your Rune Of Preservation on them and face them. (Make sure they are targeted. I try to clear my offensive target for this reason.). Both of these classes have good burst damage but after that their damage goes down considerable as they are out of AP. The 50% reduction in damage will greatly increase your chances of survival. In addition, most of their moves from the rear or side do more damage or ignore armor so facing them further cuts down on their damage. Next I usually hit shield (make sure you are targeted as defensive), followed by a HoT and then spamming Grungi's Gift. Most of them will try to circle you at this point. This is when you move out. While they are circling, take off running. Weave in and out of your own people to try and get them stuck on your own players. This will also get other players attention that hey you need help. Hopefully another healer picked up on this and is spamming heals your way also.
In addition as you get higher, WEs will hit you with a curse that will do damage to you as you move. Make sure to take this off with Rune Of Cleansing.
Remember also that your heals except your shield have a range for 150ft. This should allow you to easily heal the front line while staying out of ranged DPS damage. If it's close quarters fighting, try poping around around the corner, throwing your Mending/Regen combo and hiding back around the corner. If you feel a bit more confident throw out your Serenity too.
Well I hoped this helps some.
-Zandaris