So I hit level 70 the other night on my Paladin, Amildelais. This is a remarkable milestone when you consider I was going to delete her at level 20 and spared her simply for bag space. Time played to 70 was an unremarkable 11 days, 23 hours and 50+ minutes, but that is a record for me. I do have a tendency to stay logged in while my attention is elsewhere; obviously I have a concentration problem that contributes to my altaholicism. My first character to 70 was a rogue with just under 30 days played, and my second was a priest with almost 20, so I am learning. I thought this to be an opportune time to relate some of the things I've learned about levelling.
Always log out in an inn or major city
I don't have specific numbers, but did notice that when I had rested bonus, I'd do about 50% more XP per hour on my rogue than when I didn't. Every 8 hours you're logged out in an inn or capital gives you another bubble of rested bonus, up to a maximum of 30 bubbles (or 1.5 levels worth). I can see not doing so if the travel time to where you're questing is very long, and your time logged out will be fairly short. Otherwise, you're just hurting your levelling speed for no good reason.
Spec is important
Yes, I know, you plan on being a healer. Great. But unless you're constantly grouped with a friend or levelling in instances, your healing spec is going to take you a lot longer to level than your damage spec. I tried levelling my priest as holy for a level in the 30s, again in the 40s, and one more time in the 50s. It's true, there was a lot of survivability, but every fight was taking 1-2 minutes, and I was having to stop and drink a lot. As shadow, I found that I was killing mobs in 20-30 seconds on average, and my healing was good enough for instances into the 60s. Tanking specs can be slower to level, too, but I have to say that Amildelais was protection all the way through, and levelling just got faster and easier the higher she went. You may have to experiment to find the right mix of talents and gear for your own character, but don't deliberately cripple yourself when it isn't necessary. Having said that, I'm levelling a druid with a friend right now. He's gone resto, and I'm feral. We're doing quite well with a healer/bear combo. Stuff takes forever to die, but we can pull 5-10 mobs at a time so we make up for it.
Trade skills can be time sinks
When you play only one character, it may be important to level professions and tradeskills. Be mindful of the time you spend working on them, though. I already have 2 characters with cooking skills approaching 400, and one with a fishing skill above 400. I don't need every character to have a fishing skill of 400, since I can only fish with one character at a time. Same holds with cooking. Most crafting skills can be powerlevelled fairly quickly at high levels, so why bother spending time at low levels working on them? The items you can make and use while levelling are usually sold at a loss in the auction house by others who are working on their own crafting skills. Gathering skills are nice, but they also take a lot of time to develop. You may find it faster to level once you have an epic mount. I like having a couple of gatherers, and levelled characters while working on mining and herbalism, but I won't be working on any more. Why have yet another character mining copper for a couple of gold per stack when I can log in for a few minutes on my warlock and make much more money picking some herbs in Northrend? I do think every character should level their first aid, but in most cases you should easily gather enough materials simply from questing. The only spot where I run into trouble is mageweave, and grinding some extra ogres while questing in Tanaris will solve that pretty quickly.
These are just a few tips. I'll follow up on Thursday with more.