A little bit about myself for credibility: I am a 21 year old college student and have been playing WoW since it was first released. I have three characters at the gold cap and want to share my methods with you in a way that I hope has been more clear and concise than the other guides out there. Thanks again and check back soon for my role-playing guide for WoW as well as other guides for MMOs and RPGs in general.
A central problem of long-running MMOs like WoW is that the player's numbers have to continuously get bigger and bigger in order for the player to feel more powerful. When the original game released back in 2004, player health pools topped out in the thousands of hit points. Today, everyone is running around with absolutely massive numbers on their stat sheets, many of which have climbed into the millions. Players can deal out an equally massive amount of damage and it's gotten to the point where there are so many large numbers flashing across the screen during combat that it can be hard to keep track of exactly how well you are performing.
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.

Some quests in my guide are marked as "SKIP" and colored in red.  These quests are simply either too hard to solo or not worth the XP/time and are skipped.  My guide will only list SKIPPED quests if the quest is a direct follow up after completing a quest, not one that you have to click the NPC again to get it.  If you hover over the skipped quests, it will give info on why it is skipped in the guide (unless that info is already listed directly in the guide text).
Island expeditions are very easy to complete while leveling, particularly before hitting Level 116 when your legendaries are still in effect and your secondary stats have not been squished by leveling scaling yet. Island expeditions can be completed in 5 to 10 minutes relatively reliably while also acquiring some of the pets, mounts, and Bind-on-Equip gear available. There is also one weekly quest to do one island expedition, so for slowly leveling alternative characters, be sure to complete at least one island expedition each week.
Mag'har Orc Allied Race Leveling Guide (20-120) Dark Iron Dwarf Allied Race Leveling Guide (20-120) Void Elf Allied Race Leveling Guide (20-120) Best Void Elf Allied Race specs for leveling, efficient zones to level in, and overview of available classes and level 20 starting abilities. Level a Void Elf to 110 for a special set of cosmetic Heritage Armor. Nightborne Allied Race Leveling Guide (20-120) Best Nightborne Allied Race specs for leveling, efficient zones to level in, and overview of available classes and level 20 starting abilities. Level a Nightborne to 110 for a special set of cosmetic Heritage Armor.
Potions serve more utilitarian purposes, and it's up to you to decide whether to make use of them. The most common is the Swiftness Potion, which can provide you a handy boost in speed while going after annoying quest objectives indoors. These are generally MASSIVELY overpriced, because people know how useful they are. I opted not to spend the gold since Warriors are already fairly mobile, but slower classes may benefit greatly from these.

Most of the players make the mistake of only listing 30-50 transmog items on the auction house and then hoping to get half of them sold until the next day. Me and a lot of other gold farmers and transmog sellers do have 3.000-10.000 items on the auction house across various realms. It does not mean you have to do it that way – but if you have 1000 items listed, chances are higher you can sell up to 10 per day. With only 100 items listed, you have to be lucky to sell one. Of course, the sells are not guaranteed if you post more items. But i’m sure you have a lot more fun if you open your mailbox and 10-20 items are sold