I'm going to be playing with my other half when it's released and I'm fully expecting it to take 3 or so months at least to get to 60.
Just going to quest all the way through.
Group quests together, complete them in chunks. Find a good leveling route with quest areas.
For extra ease, play a class you can solo well with. Hunter is exceptionally easy to level.
Hunter, Druid, Mage and Warlocks are the easiest to lvl up.
Rogue, Priest, Paladin and Shaman are next in line.
Warriors are the most annoying and difficult since their entire class is "Take dmg to do dmg", which is so bad for lvling up.
The one pro thing about Warriors are that they can tank so well in dungeons and it's easy to find groups, so if you level a warrior. Google and make sure to get all instance quest and focus on them when possible. Good gear and good XP. Also, when you're lvl 30 (if you're slow) get a friend to boost you to get whirlwind axe ASAP. It's a weapon good enough to get lvl 60 with, and you get it already at lv l30 from a quest chain.
Otherwise, overall tips. Study some guides, maybe lvl 1-2 toons on private servers. Barrens is awful, go to undead areas to lvl up as much as you can if you're horde. Alliance quest flow is amazing and easy.
questing is how i am gonna do things, there are so many zones and cool stuff i probably forgot about
lets not forget how long it took to get dungeon groups, and have them fall apart mid BRD!