Buffs. Food/Flasks/Scrolls/Potions/Elixirs are a small, but noticeable, buff to your killing speed and survivability. If you have a max level character that can already supply you with cooking or alchemy, you'll be very well off, because the AH is a cesspool for this. I can't really give you specific foods or potions to look for, since each AH is going to have different supplies. Generally speaking, lower level foods are going to only last 15-20 minutes until you can buy the more powerful versions at 60+. Look for anything that adds versatility or your primary stat, and buy stacks for each level range(1-60/70/80/90/100)
101+ At this point you'll start taking a penalty on quest/bonus objective experience for every level past 100. Treasures, however, remain worth their full value all the way through level 105, at which point they'll be worth something like 15% less, and then another 15% more when you ding 106. I recommend that you stop questing/gathering entirely, and collect all the treasures you can stomach, only avoiding any annoying to reach ones inside caves or behind elites/rares(where scaling does bizarro things).
Quests from the Tortollans, a race of turtle people, can be mind-numbingly dumb and slow. One of the standards that you'll see is one of those matching games arranged in a grid where you can only turn over two items at once to see if they match. Another, and the worst of all the quests I've done in 13 years with World of Warcraft, is a turtle "maze" where you slowly guide a slow-ass turtle through a slow-ass grid for seemingly no reason other than to get a reward at the end.
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.
Edit 20 It’s been a week since this post and a lot of people are still reaching out to me with questions which is fine. I have had a few different people reach out to me to help make YouTube videos based off this guide and more info in BFA which I’m more than willing to do. Whoever gets the videos up first I will link them here for you guys to enjoy.