A Mythic+ dungeon is a much more difficult version of the original, and loot doesn't drop directly from bosses; instead, a chest will spawn at the end containing a number of items that will increase depending on how quickly you cleared the zone. The level of this loot will increase based on the difficulty level (Keystone) of the dungeon you completed, starting at 345 and scaling to 370 for a M+10 or higher.
If you queue as a healer - take care to always have a stack of water of appropriate level. You can buy it at an innkeeper for next to nothing, but remember that it will become too low-lvl for you very fast, so you need to buy new water every 10-20 levels. Alternatively, you can buy a stack of every tier of water in Stormwind, and just always carry it with you. Another alternative, if you see a mage - always ask him (politely) to create a table for you. Grab 2-3 stacks so you have extra for the next runs.  
The World of Warcraft playerbase is cut in half, but not in the usual “Horde versus Alliance” fashion. Instead, Horde players themselves seem at odds with what their faction actually stands for. Cobo and Lo suggest that this mismatch may be hard, if not impossible, to fix. Someone is always going to be disappointed, and with Cobo’s talk of honor being at the center of the Horde, Sylvanas-stans will probably have a disappointing time with the expansion.
Leveling used to be a treat in WoW. New, unique abilities drove you forward and made getting past the horrible grind worth it to some extent. Now it just feels like everything is set to grind. More than it used to be. Once it was tolerable, rewarding even, but now you grind to unlock an allied race through reputations barely connected to most of these races, only to have to level up that character to get their unique armor set (compelling you to not just boost your character and instead suffer through the slog of ANOTHER group of alts), then you get back to current content and grind some more with a random chance to drop the item you need to get your ilvl up to finally enjoy the single warfront available (as I write this).
Special mention is the Darkmoon Faire Top Hat and WHEE! buff. While not always available due to the DMF being inaccessible most of the month, if you happen to be leveling when the DMF is running, it might be worth your time to go and get these. AFAIK they do stack with heirlooms, although I have not personally tested it. Fair warning: These buffs do NOT stack with each other, and the hats disappear after the DMF goes away later in the month(unless you only log in when the faire is running).
Certain locations in World of Warcraft – primarily inns, capital cities, and private instanced zones like your garrison or class order hall – are rest areas. You know you’ve entered one because your character portrait will gain a “Zzz” icon where your level is normally shown, and because you can immediately log out of the game instead of waiting 20 seconds.
The term “role-playing game” also means that you play the role of a character that lives in a fantasy world. How deep you connect with the character – is up to you: some people come up with habits, manners, and the whole biography of their game counterparts. Diving into the virtual world can bring a lot of fun, but the choice is yours – perhaps such a game style simply doesn’t suit you. This role component is voluntary, but we provide some role-playing worlds for those, who prefer to play with a full immersion in the world.

The guide should advance to the point where you are in the zone's progression. There are a few steps that can-not autocomplete and they should (hopefully) have comments to the effect of -- you need to manually check this step off. -- For some reason you have to click these steps off 2-3 times to work. (the first time will move the tom-tom arrow, the 2nd time unchecks it and the 3rd click advances the guide).
We’ve spent a lot of space giving advice for those with less experience in the nuances of World of Warcraft. If you’re a player who generally knows how to get around the game—or did at one point—you’re probably still going to feel a little stuck if it’s been a decent amount of time since you last played. For example, why does your favorite weapon no longer work the way it used to? What’s the latest currency you have to know about? Should you ever waste time hanging out in your Garrison again?

Some dungeons are also much better than other. Some take a long time to finish and some are quick. Some have few quests and others have many. The ideal dungeons have a lot of quests and are quick to finish. If you are sent to a long dungeon that you have already completed, you can leave but you won’t be able to enter a new dungeon in 30 minutes. Dungeons like the Stockade are super quick, so it will still be good XP if you are sent here more than once.
Anyway both got to 110 at around 50h played. I messed up with my Pal by going to Legion once I hit 100 instead of finishing treasures and bonuses in WoD. All in all, if I picked the best zones and was only trying to level as fast as I could, I would probably could have done it in roughly 40h. Note that it would have a been A LOT faster with a Monk as both Ret and Rogues don't really have a decent AoE until 40+ (45 for Ret and 63 for Rogue I believe). The daily also helps a lot. I know that leveling my Monk before the pre-patch was insanely fast. Might be slower with the changes to FoF, however.