Let me just start that this is not really a guide. It is some insight into leveling the class as well as some of my personal experiences while leveling. You will not see fancy math and such.
I have leveled my Druid as Resto since day 1. I was going to say level 1, but you dont get to choose talent points until level 10 which means you are just a jack of all trades, master of none. For most Druids, the first few levels are extremly difficult compared to other classes. You basically have a nuke and a dot and a few heals. It seems to take forever to kill things. Most Druids agree that at the very least, you will die a whole lot less once you get Bear Form. Most Druids I know have leveled up as Feral and kitty critty killed things.
The first 10-12 levels on my Druid were solo. Then I decided to do RaF and rolled a Rogue to run around with my little tree in training. They leveled together all the way to 60, with the Druid throwing HoTs on the Rogue and the Rogue sinister striking everything in sight. Once I hit Outlands, I basically instanced from 60-70 with a few quests thrown in here and there (most notably the dungeon quests).
While leveling as a Resto Druid, I think it is important to do about and even amount of dungeon leveling and quest leveling. Dungeons get you better gear so that you can kill things faster (but still pathetically slow). You get a ton of XP from these dungeons and you get to learn you role as a healer. This is where you learn what heals work best in each situation. I like to level in dungeons when I have rested XP. Quests are important as well because even in you do not have rested XP coming to you, you can make a lot of progress very fast.
While out questing, entangling roots are you best friend. You root your target in place, Starfire, Starfire, root, Starfire, Starfire, rinse and repeat until you have killed all of the nasties you need for your quest. Always make sure you are buffing yourself with Mark of the Wild and Thorns. Thorns are mostly valuable to you when you are questing and you end up fighting more that one mob. If the mob is immune to be rooted in place, and they are going to be beating on your face, throw a hot or two on yourself and moonfire/wrath your way to victory. In this situation, Wrath is a better choice as it has a shorter cast time and will not get knocked back as many times.
While you are out questing, put yourself in LFG. You will often times get into PuGs, which really is the best place to hone your skills. This will also let you keep an eye on the LFG channel for any interesting opportunities.
I would also recommend at least a little bit of PvP. Specifically battlegrounds. Since the expansion I have become a PvE player predominantly, but the skills that you learn in PvP can help you greatly when you are out getting your quest on. It teaches you how to CC, how to heal on the run, and when to fight and when to run.
Last night I actually got a bit over half a level on my Druid. I logged on, and immediately put myself into LFG. About 5 seconds later I got a blind invite from Over Eager Mage to do UP. Apparently Mr. Eager does not bother asking spec or looking at the notes in LFG as he more or less just hoped I was resto. To fill out the group, he grabs a Warrior to allegedly tank. Once again, he did not pay attention and I called them on the Warrior's 17k HP and Arms spec. They wanted to give it a try with him tanking despite the fact that we had an 80 DK with 19k HP in his DPS gear. I died on the very first pull and immediately let them know that this was not going to work out.
The DK switched into his tanking gear, and we only had one death the rest of the run (Mr. Eager ran ahead into a room where a patrol completly owned him).
After the run, I put myself back into LFG and Mr. Eager asked me if I wanted to do CoS. I said sure and got an invite. Of course he just starts randomly inviting anyone he can. We got a level 80 tank, who despite being completly new to tanking actually did a pretty good job during the run. We also got a DPS DK and a Holy Paladin. Yes....a Holy Paladin. Mr. Eager did not see it as a problem to have two healers. This run seemed to take forever. From AFKs, to the fact that we were basically short a DPS and everything in between. Overall, there were only a few deaths here and there, and one wipe on the first boss. The Paladin was only doing about 200 DPS, so I told him that I could do some DPS if he would heal.
Well, his healing was not exactly stellar. Basically, for the rest of the run, we ran one and a half healers. I was the one, and he was the half. After a while, I checked the meters and noticed that I was doing about 970 heals per second.....he was doing in the 300s. I decided to keep an eye on him. Basically, he only casted flash heals like he was playing in BC. He also did not spam the heal. He would heal.....then sit around a bit....then heal. I must also note that he never bothered healing himself or anyone but the tank.
Despite this crutch, we got through the run, albeit very slowly. At the end of the run, the Paladin was rocking 400 HPS. I feel sorry for the group that he main heals down the road. After that, I did a good chunk of questing in Dragonblight and got about 10 more points in inscription.
Another reason that I am so keen on leveling partly in dungeons is that you end up with more quests for cash at the level cap. I will most likely hit 80 by the time I finish with Dragonblight and have only completed Borean Tundra and Howling Fjorde to this point. Once Dual Specs come out, I will be very happy to knock out zone after zone for the proverbial phat cash.
Anyways, it turned out to be a bit long, but I hope it was at least somewhat helpful!