Let me first say I don't think its the actually gameplay that makes leveling in World of Warcraft hard my opinion it's the traffic. At least on my server it seems like no matter what area I am in theirs ten other people doing the same things I am doing. Don't get me wrong I love the interaction with people, but when you have an hour or two a day to try and level you character it can get a little annoying. Here our some things I have learned when trying to get some experience in quick.
Questing - The main Source of experience now days. It used to be before a lot of the patches came out grinding was the way to level, but now Blizzard made them a lot easier to complete faster and not run along all day doing one quest for 50 experience.
Distractions - Friends list can be a deal breaker on this one. I can't tell you how many times i have seen the same person sitting at a quest hub while I just completed a group of quest 20 minutes later. Try and keep focused I personally have way more fun playing with friends when we both our at max levels doing dungeons and raids.
Ask for Help - If you have a level guide you will probably not ask for much, but if you don't just ask other people in the zone with a /who if they have done the part you on.
Grinding - To put it simply don't do it. Like i said before questing is where you will get the bulk of your experience now days. Not only that you will have a lot more fun doing different quest then killing harpies till your eyes go blind.
Organized - One way to stay organized is when you loot items that you will be selling try to mail them to your alts when your get done with a round of quest. I like to have one or two characters just for auctioning off loot. Makes it much cleaning for items you need to find in your bags. Plus I have a little case of ocd so maybe it's just me that finds it annoying.
Those our just some of the ways to get your character to level up a little faster. In the box below our more detailed guides for both factions.