"The way the glyph market works on most realms is that there are a couple of people willing to put in the long hours who will have every available glyph posted profitably, and undercut within minutes of being undercut. They all reduce the price very minimally when undercutting, and the "competition" isn't about price, it's about who can relist more frequently.
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)
You should equip new quest rewards when their item level starts beating out your previous set of gear. If you are currently wearing Tier 21 gear, it is best to let the quest rewards significantly beat your existing item level before using them. With that said, you will unlock Azerite pieces early on, which are worth using over Tier gear in most circumstances.
I tell you my experience. I'm leveling a priest that it's 60 now and since I have also done some instances (and I have full heirloom set with 20% experience gain bonuses) and been very ahead of the guide, I skipped some zones since they were grey quest for me, well it was a real mess. Missing quests because I didn't to the previous to enable the following. Going in a zone then realizing that I couldn't do that quest because I didn't do the starting quest chain, very unconmfortable. In short what I suggest you it's not to skip areas, or make really sure that you do all the quests required (at least) and check carefully the previous zone you'll going to skip to make sure that you won't have problems with struggling finding where to start the quest chain to sync with the guide section.
At 96 the standard wisdom is to immediately drop what you're doing and proceed to Spires of Arak and do the quests to unlock the Inn, granting a further 20% experience bonus while in that zone. You'll want to do that eventually anyway, but I'm not sure it outweighs the quest experience from Gorgrond. However, if you decided to go to Spires immediately at 96, restrict yourself only to bonus objectives and again leave Treasures until you're 100+. Make certain that when you being the quests to unlock the inn, you speak with the quest NPC to also learn Archaeology, since it's required to collect several of the treasures in Spires.
Make sure you have the two Flight-Path toys purchased, as this can save you time. It won't have EVERY flight path, but will have major locations for faster travel if you need to switch zones entirely(which you will). If you buy the toys on one faction, it unlocks for the other faction as well. So don't spend double the gold! These toys can be found at the heirloom vendor(Undercity for Horde, Ironforge for Alliance)
As Blizzard calls it stats were "squished," and now players are finding it harder to level with that same scaling system. It's a two-fold issue, and game director Ion Hazzikostas isn't quite sure how to fix it yet. In a massive forum post several days ago he plainly explains the issue from the start, noting that "the feel and pacing of the level-up experience is a top priority for the team."
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First up we have patch 7.3.5, which was implemented several months ago as a major shakeup to how leveling was approached. Instead of going from low to high level zones like the way the game had always operated, Blizzard opened up the map with more of a Guild Wars 2 type system -- you now have more of a choice of where to go with a scaling mechanic. But when combined with 8.0's massive stat overhaul, things got murky.
If the new Battle.net balance has given rich players a new incentive to liquidate, and the spiking prices are a result of them trying to sell all their gold at once? Prices for tokens could settle much lower once that stash of gold has been depleted. This seems likely, because there’s a compelling new reason to sell gold, but no new reason to buy it. Blizzard has a good way to drain those gold reserves from the market.
As you're leveling, I generally recommend you just follow the natural flow of the progression through each zone. They're laid out fairly reasonably. But don't be afraid to hop around, especially if you're near a quest objective. You shouldn't actually need ALL of the zones listed to reach 62. Pick the ones you like best. It's much more important to simply be as focused as possible and flow from one quest to the next.