For Alliance it's Lok'Modan, Redridge, Darkshore, Felwood, Stranglethorn (both parts), Plaguelands. Somewhere between 3 - 3.5 of these get you to 60 in like a 16 hours /played, if you queue for dungeons at the same time. I recommend dropping everything at 45 and going to Darkshore-Felwood if you didn't do them yet - they are literally the fastest levelling zones in the game right now, maybe only trumped by Silverpine.
Get exalted reputation with every faction you can. This relates to the previous two pretty directly. Gaining reputation with most of the factions of Kul Tiras and Zandalar will allow them to sell you high-level gear, while gaining reputation with the Champions of Azeroth faction will grant you levels for your Heart of Azeroth, the neck piece where all of your AP is stored.
When you have completed your third zone, you should be nearly max level, but you still have work to do! Head back to your faction hub and complete the last foothold quest to unlock your fourth mission table champion. After, you will want to do your newly available invasion missions for your faction. This quest chain is one that will be time gated by reputation levels earned with the 7th Legion for the Alliance and iThe Honorbound for the Horde. Complete as many quests as you can and then finish up your leveling with side quests you may have left in previous zones as necessary.
Even if you don’t have flying in WoD be sure to get the WoD handy notes. If you have flying simply fly and pick up all the treasures that you can and do bonus objectives. Not every single piece of treasure will be worth it though as some are hidden in caves or are just hard to get. So if you find yourself spending more than a few minutes finding a treasure, just skip it and move on, there is plenty of treasure to go around.
Changes were also made to levelling in earlier content with Legion's 7.3.5 patch. The level-scaling tech introduced in Legion not only be continued in the new continents of Kul Tiras and Zandalar, but was also be applied to content from prior expansions, allowing larger level brackets for lower level zones. Further, as previous expansions are now included in the base game, the level ranges for those expansions are now broadened, allowing players to spend more time leveling in preferred expansions and avoid others entirely. Some examples include a zone like Westfall having its level bracket (at 10–15 as of Legion) increased to 10–60, whilst continents such as Outland and Northrend sharing a 60–80 level bracket. The aim of this change is to encourage more player choice whilst levelling and to allow players to experience the full story of a particular zone without overlevelling the relevant quests.
Havoc in Battle for Azeroth has gone through somewhat of a maturing process, trying to focus more on the talent tree and allowing for more diverse options in gameplay approaches, alongside tightening up some of the more loose aspects of the original implementation. It still remains a predominantly builder spender style rotation and is largely Global Cooldown locked. The core hook is making the most of your Fury pool and reacting to unpredictable gains, ensuring you use high burst cooldowns and windows to push yourself even further. On top of that, it comes with a variety of mobility and defense tools, creating a versatile toolkit with some unique abilities that can be used in a variety of ways.
Drustvar is far and away the hardest Alliance zone, which is exactly why you want to do it first. If you have legendary items, they’ll still be usable, and if you don’t, this zone will still be easier early on than it will be later. Drustvar is also extremely fast and will let you jump out ahead of your competition in other zones, which means fewer players around to take your quest objectives.
Incursions are a new world content activity that are unlocked when one character has unlocked World Quests. This feature is unlocked account-wide meaning that all characters on that account can access Incursions even without being Level 120. This provides for a lucrative experience acquisition method that is available in a similar pattern to what Legion Invasions offered with nearly an entire level earned by completing an Incursion series which involves four World Quests and one mini-scenario at the end. These also grant item level 370 weapons and Azerite armor, so they should be done any time they are up. Incursions follow a similar schedule to Invasions and are available for 20 hours once they are initiated.
Sometimes that requires players to earn gear to give them greater powers that they haven’t yet unlocked. That sense of progression is at the center of what makes World of Warcraft great and so successful over the last 14 years. There should always be a balance between gaining gear and strength through lower-level content and taking on the hardest challenges the game has to offer. With Battle for Azeroth, Blizzard has missed the mark. Getting to elite status just requires grinding content that isn’t fun, instead of players demonstrating their skills.
Dugi’s leveling guide is the leveling addon I’ve always used to level as fast as possible. It will show you where to go and what to do in-game, speeding up the leveling process. This is optional though, as the game already does a pretty good job at showing you where to go at all times. The addon does, however, come with a couple of other nice features and perks.