Once you reach an Alchemy skill of 475, you may begin a quest to learn one of three specializations: Potions,Elixirs or Transmutations. Being specialized gives you a chance to create an extra 1 to 4 (for a total 5) items while crafting in the field you have selected. For example, a Master of Potions may be able to craft more than one [Super Mana Potion] for the same material cost as one.
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.
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-New dungeons- About 3/4 are fairly decent, not too long not too short, but none of them are compelling, none make me say to my friends and guildies, "Hey, let's do this instance, I love the theme and encounters." They're dull but tolerable. The other 1/4 of the dungeons just aren't fun and you will groan when you get a mythic Keystone for the Underrot, the snake temple, or Waycrest Manor. Waycrest Manor is actually one of the better dungeons, however, with the new Infested affix, Waycrest Manor suffers from many game-breaking bugs that end in the entire instance being pulled due to doors not properly working as intended.
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.  
Tiragarde Sound and Stormsong Valley are both fairly similar zones, but Stormsong is a little longer, meaning that you might not even have to finish it to hit 120. Tiragarde also comes with a bit of a warning. There are plenty of side quests to do in the zone after you finish the story quests. Don’t do them. It’s not worth the time or the experience you’ll get.