Professions: This may seem strange for a leveling guide, but the first opportunity you get, pick up both the Mining and Herbalism gathering professions. Not only will this allow you to track many various quest objectives on your map, but you also get a fair amount of experience whenever you gather. I'd put it at around 10% of a quest turn-in per gather. Since most of your wasted time in WoW is travel time, stopping to gather ore or herbs can keep your exp/h rolling as long as you don't go too far out of your way. You should only gather if it's convenient, and on the way to an actual quest objective. Don't make gathering your priority. 

Two new raids will be introduced in the update, which differ drastically in size and content, depending on which side of the war you’re on. The Siege of Zuldazar raid will see Alliance players trying to take over a city, but if you’re part of the horde, your version will see you try to defend it. Once you’ve beaten it once, you can then play the other side. The Crucible of Storms raid, on the other hand, is smaller, and only consists of two bosses.
To use it as a bag-space creator, simply send excess items to the bank alt whenever you're near a mailbox for a low price of only 30 a slot. Even if you accidentally send the wrong item to the bank alt, it can be returned-to-sender for free. It's very quick, due to the fact that sending mail between characters on the same account is always instant.
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.

You should try and quest efficiently - pulling several mobs if you can handle it, using your burst cooldowns while questing to kill everything faster. Many people would think that a 10-minute cooldown like Bloodlust is useless in open world, but you can do a "kill-15-mobs" quest in like 30 seconds if you pull a lot and use it. A free quest every 10 minutes is not that bad.
First of all, the value of transmog is decided by rarity and how they look. Some items like Minenarbeithut der Tiefen or Pendel der Verdammnis (they can drop in Uldaman) are worth millions of gold. They are worth so much, because they have a really small chance to drop. Other items are bought well because they look good. Best example in this case is the Glorious set, its legplates Glorreichen Beinplatte reach a 100.000 Gold value easily.