Picking up herbalism and mining is the best professions to have while leveling. Not only will you earn gold as you level, but you will also get extra XP. At level 20 you will get over 500 XP for picking up a ore or a herb while killing a mob only gives a little over 100 XP. Don’t go out of your way to pick herbs if you are trying to level quickly, but pick the ones that are on your way. Leveling from 110 to 120 can be done pretty quickly just by doing this. There are a few items that will help you if you decide to use professions while leveling:
There is a constant market for transmutations. If you are capable of doing these, you can charge an upcharge on each of those transmutes. A player who logs on his/her character each day, and sticks to it, can generate a significant subsidiary revenue scheme through transmutes. Likewise, if you have a transmute that allows you to transmute a lower value element (such as Earth) into a high-priced one (like Water or Fire), you can make a cool 15-20 profit every day by simply doing your transmutes.
It’s a name lovingly given to me by my little boy, when he discovered I owned 1/4 of the wealth on the largest server in the EU.  I’m proud of that, not arrogant.  You can be “royalty” too if you put the effort in and refine your skills.  One day, someone will become the Gold Emperor, and I will be extremely proud of them.  That’s why I created a Hall of Fame, so you can journal your way to the top, see how far you’ve come, and be inspired by other member’s progress.
Island Expeditions:[5] 3-Player co-op with optional 3v3 gameplay. Players will explore uncharted isles across the Great Sea. There is azerite and other unclaimed resources bubbling to the surface that is highly sought by both factions. Complete varied and dynamic objectives with a large variety of challenges to overcome. Race against advanced AI opponents designed to thwart players using tactical and strategic moves that consistently change. Optionally, players can choose to race against other players, creating a 3v3 PvP environment. 
This top-end difficulty was missing entirely from Legion’s first raid, Emerald Nightmare, which was cleared by top guilds in around 11 hours. Meanwhile the first guild to clear Uldir’s hardest difficulty, Mythic, spent somewhere around 70 hours attempting to kill the raid’s eight bosses. Even after all that time, the guild, Method, still had members say they loved the raid, and that it was one of their favorite in recent memory.
Congratulations on reaching Level 120! There are a myriad of new things to do. The first thing you should do is head to your faction hub ship where you have been doing your mission table quests and footholds to pick up and complete the quests necessary to unlock World Quests. World Quests will provide you an opportunity to grind reputation levels, acquire gear, and gather Azerite. There are tons of new things to do that we will cover in our Level 120 Battle Guide found here: Level 120 Battle Guide.

Swim Speed Potions (used especially at lvl 37 for Faldir's Cove in Arathi Highlands and lvl 57 in WPL).  Try to get multiple stacks of these.  I also recommend keeping a stack of these always in your bags.  You will frequently pass rivers and lakes and can use these potions to pass them faster through out the guide.  Please note that these potions do not stack with Druid's Aquatic Form and Glyph of Aquatic Form.

The old popular example was the http://www.wowhead.com/item=47257. This item differed on my server from a high of 6k to a low of about 3k. When the price was down at 3k, I would buy a few of these and just wait a week. Throughout the week, I would put in trade and the auction house that I wanted 6k for it. I would then immediately go onto an alt and say that I only wanted 5200g. Sometimes, I would get the 5200g and be a very happy man, other times it would take more patience. However, almost always, by the end of the week, the other sellers had reposted for around what I wanted. This gave me a huge advantage. Now, the price ceiling was no longer 3k on the auction house, but 5k. I could now easily sell the few I bought for 4 or 4.5k, which is a huge 50% profit from the 3k I originally invested.

A "stat squish" and "item squish" was implemented to lower the numbers used in the game, e.g. a legendary item previously with a level of 1000 reduced to 265. Unique class-specific buffs are added back, i.e. mages' Arcane Brilliance and priests' Mark of Fortitude. Titanforging—a random event that raises the initial item level of an item gained via drops or rewards—is still in the game; however, if the item is one of those affected by the Heart of Azeroth, then that item cannot be titanforged.

I recommend not counting on transmog sells for your monthly gametime. Its a great market, but also pretty random. You have to have the right items posted at the right moment if a player needs a certain item. If this is not the case, of course you will not sell anything to him. There are people making millions of golds a month with transmog. But they are very professional at it and it really takes a lot of time.
Much like an encounter with a wild pet team, PVP Pet Battles are turn-based. However, unlike the PVE version, the PVP combat system is timed and any ability for each round must be chosen within that time limit otherwise it will assume you have passed a turn. A time penalty is applied if you take more than 15 seconds to choose an action, resulting in progressively shorter round timers for you.
In player vs. player designated zones, you will still be viewable and attackable by players, but you are not left completely defenseless. While engaged in a Pet Battle, any attack from another player will break you out of the battle. You will receive a 3 second damage shield that will absorb 50% of incoming attacks. The same exact wild pet that you were previously battling will respawn after you come out of combat with the other player. However, if you defeated the primary pet in battle prior to leaving the match, the pet and its team will not respawn.
Quality gear. These can be greens, rares, whatever. However, always think, "Who needs this?" Items that have stats like Stamina are typically useful to all players. Items with stats like Spirit are only useful to a subset. Items that combine two highly sought-after stats, like Stamina and Intelligence (which all casters need) will sell for more than items that combine two stats like Agility and Spirit (which practically no class needs).
It's hard to step out of the shadow of Legion, which was utterly fantastic in almost every way, to enter an expansion where you get one item per boss in the last expansion because the rules have been changed to force more grinding, where you have to grind reputation in the old expansion that you probably skipped because rep grinds suck JUST to unlock allied races (who aren't fully unique races since they recycle old content such as animations), where questing has SOMEHOW become boring again and where your new abilities are given by items you'll swap out every level, meanwhile being only boring passive effects no one cares about.
Elemental items (Primals, Eternals, etc.) can be a good source of money, because they are always in demand on the AH. See which mobs you will most benefit from farming, then set out for a few hours. In the process you will also most likely collect significant vendor trash, and may get other profitable item drops as well. Note, however, that older elemental drops usually lose profitability compared to newer ones, i.e. Primal Water sold well to level 70 players in BC, but sells far less well to level 80 players in WotLK, because level 80 gear requires Eternal this'n'that.

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A cool little pet farm that can take minutes or ages depending on the god of luck.  This spot contains some of the most dense troll spawns in the game, and each has the highest chance to drop the parrot pet thats soo sought after.  On every serve rthis per has  amedian value of about 70,000g so picking one up can be a pretty cool feat.  Like the sprite darter hatchling spot its, a random farming spot that requires alot of RNG to pull off, but if you get it to drop you can make out in spades.  The other drops are miniscule when compared to this spot.

This leaves players chasing an endless loop of trying to get higher level Azerite gear — which can only reliably be gained through raids and isn’t available in Mythic+ — but only the pieces with exactly the right traits will actually be an upgrade. It’s even possible that some items that should be huge upgrades are nullified by the loss of a specific trait that makes one ability do more damage than the others.

While leveling, try to make use of the new Battle of Azeroth experience gem, Insightful Rubellite, which gives you +5% experience. Equipping one of these requires a socket in your gear, so try to hold on to a piece of Legion gear with a socket or acquire one of the Legion Legendary rings since every class has one. Each of the rings includes a socket. You can acquire one of these rings rather easily by doing World Quests in Legion zones and acquiring 1,000 Wakening Essences that can be used to purchase a legendary ring in the Legion version of Dalaran.
1. Don't just take anybody with some gold willing to go. Make sure they at least have some heroic gear or better. Bringing someone in greens not only hurts your chances of killing the bosses, but these players often anger those who are in better gear that need one item and then get outbid by some "noob". You are looking again to establish relationships and repeat customers!
Even though the guide was developed with a hunter, the guide can be followed by any class.  Except you have to do your class's quests which aren't a whole lot.  I do have full intention to make my guide friendly with all classes in the future by listing all of their steps as well.  There will be a toggle that allows you to show which class's steps you want to see in the guide.  But this is coming later.
Through out the game, the quest log will be capped to 20 many times.  The guide makes use of maximizing the total amount of quests you can accept at once.  Because of this it is important to follow the guide exactly and only accept quests if the guide tells you to so you won't run into issues not being able to accept a quest.  If you do accept a quest that is not listed in the guide, write it down because you may need to abandon it in order to keep following the guide if your quest log is full.
Anything that can be answered by reading the recent discussions on the subreddit, has a yes/no response or can be looked up on sites in the community resources should not be posted in a thread of its own. Questions such as 'What is this worth?', 'Did I make a mistake?', 'What do I do with XYZ?' or 'Should I buy/sell this?' will be directed to the Daily Questions sticky.
Most classes in World of Warcraft start at first level, but Death Knights and Demon Hunters are exceptions. They start at level 55 and 98, respectively. This alone can shave a huge chunk of time from your leveling experience. Of course, it only works if you want to play a Death Knight or Demon Hunter, but they’re both solid classics that can dish out damage or tank in a group.