Gold for riding training. Travel time is a SIGNIFICANT time sink while using quests to level. You don't want to wait to get it. In fact, while questing, the second you ding 40/60/70/80 you'll want to hearth and train it IMMEDIATELY! 10304 gold is the base cost, which will be modified by reputation. Also, make sure you're in a guild with the 10% riding speed bonus unless you're a class that already gets a mount-speed buff.
Update: The reason for less experience from gathering is due to how Blizzard revamped professions and broke them down by expansion. In order to get full exp from gathering you'll simply need to find a profession trainer for the relevant expansion. (WoD you just mine or herb the first one ypu come across and the game gives you a scroll for learning WoD gathering).
Meanwhile, on the island continents introduced in the Battle for Azeroth expansion, players level 110 and above who have unlocked world quests can participate in Faction Assaults. These special events, alternating between Alliance and Horde territory, will give each faction a chance to band together to defend their territory or invade their enemy’s via a series of world quests. The prize? Survival! Also faction, gear and gold. Maybe even some pride.
NOTE: It is VERY important to not vendor any equipment you pick up. You will be deconstructing all of your gear for resources that will help you in the Warfronts to be fought! Deconstructing, or scrapping, your gear will be done using the Scrap-o-Matic 1000 if you are Alliance and the Shred-Master Mk1 if you are Horde. This works the same as the way the Obliterum Forge worked in Legion. The scrapping feature can be used on all Battle for Azeroth equipment found, not just craftable equipment, so save everything you acquire for the scrapper! Before we get started, keep in mind some of the tips below that can speed up your leveling process!
Almost all quests in a zone will award reputation for that zone's faction. Be sure to go back and do all of the side quests in a zone in order to maximize your reputation gains. More reputation means more and faster access to gear and other world content. Each day, you should prioritize doing all of the World Quests that you are able to do, especially the ones in on the opposite faction's island for 7th Legion or Honorbound reputation in order to unlock the ninth Mythic dungeon and all parts of the War Campaign. Maintaining your mission table and champions will also prove to be a fruitful method of reputation acquisition as your champions and troops work passively to acquire reputation rewards while you actively earn reputation through World Quests, island expeditions, and other means!
REDISCOVER AZEROTH AS NEW ALLIED RACES – Take a new form for your adventures as new playable Allied Races. Embark on a quest to earn the favor of the Lightforged draenei, Highmountain tauren, Nightborne, Void elves, Dark Iron dwarves, and Zandalari trolls to unlock each race and add their strength to your faction. Create a new character and complete the full leveling experience to earn a distinctive Heritage Armor set.
Island Expeditions: 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.
If you queue as a healer - take care to always have a stack of water of appropriate level. You can buy it at an innkeeper for next to nothing, but remember that it will become too low-lvl for you very fast, so you need to buy new water every 10-20 levels. Alternatively, you can buy a stack of every tier of water in Stormwind, and just always carry it with you. Another alternative, if you see a mage - always ask him (politely) to create a table for you. Grab 2-3 stacks so you have extra for the next runs.
Level 120 comes and goes. Island Expeditions have unlocked, but it turns out they’re not much fun, and the most rewarding versions are only accessible to premade groups. You turn to Warfronts only to realize they’re not available this week. Fine. You can always grind out better gear. Except as you do, you notice your new gear has higher Azerite requirements than your old gear, which means your shiny new items have fewer unlocked traits than what they replaced. Discouraged, you decide to roll as one of the cool new Allied Races. Except you can’t because they’re all locked behind reputation grinds.
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).
These guides are completely automated and work in-game, so you can see step-by-step instructions as you play. The guides automatically move to a new step as you complete the quests. You are told where to go i.e. the questgivers for accepting and turning in quests along with where and how to complete the quests. Zygor has more steps and details, which would be more suited to beginners. Dugi condenses the info into fewer steps, but still has all the necessary questing info.