Even though you will invariably do a bit of soloing during your time in World of Warcraft, the game is a lot more fun when you have other people to interact with. Whether you’re starting out, or getting back into the swing of things, having helpful mentors feeding you suggestions (or gear, or gold) doesn’t hurt. The /r/wownoob subreddit is a good place to find friends to quest with, as is the main World of Warcraft subreddit (and don’t forget its helpful “Murloc Monday” thread for newbie Q&A).
I highly recommend actually staying in the 20-60 range zones until you ding 62. The reason for this is that despite getting a slight penalty in experience for being over-level, the advantage of having flight will more than offset this. That, and WOTLK and TBC zones are the slowest part of the leveling process. Minimizing your time there as much as possible is worthwhile.
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!
The best way to collect AP is through world quests, a system that allows players to complete menial tasks to earn moderate rewards. A finite amount of AP spawns on the map through these quests — generally at least 2,000 a day. I’ve likely done most of these quests close to 20 times in the course of preparing my various characters in the 45 days since the expansion launched. In some cases, I’ve replayed them as many as 50 times.
Some people have made arguments that quest blues can sometimes be more powerful than heirlooms, especially with sockets. I'm not convinced. The simple fact that you never have to even look at quest rewards will save a non-insignificant amount of time over the course of leveling. Also of consideration is the value of enchanted gear never having to be re-enchanted.
The World of Warcraft playerbase is cut in half, but not in the usual “Horde versus Alliance” fashion. Instead, Horde players themselves seem at odds with what their faction actually stands for. Cobo and Lo suggest that this mismatch may be hard, if not impossible, to fix. Someone is always going to be disappointed, and with Cobo’s talk of honor being at the center of the Horde, Sylvanas-stans will probably have a disappointing time with the expansion.
To give you some perspective I leveled both a LF Ret Paladin and BE Rogue (so one started from level 20 and the other from level 1). I focused on getting the achievements I was missing for the Loremaster, so not the most efficient route by any means. I was using full enchanted heirlooms (minus the ring) and the WoW-Pro addon though, as well as having War Mode turned on all the way.
Taking Herbalism and Mining as your two professions can be a lucrative way to level with the very stable and high prices of herbs and ore thus far in BfA. While rested, each mining and herbalism node will award nearly 4,000 experience points which makes it so that four to five herbalism or mining nodes is equivalent to one quest. If you have the Sky Golem mount for herbalism, you can pick herbs without losing mount speed. There are also enchantments for gloves that will increase the speed at which you can process the herbalism and mining nodes. These can be made rather easily by an enchanter and should be relatively inexpensive on the auction house. These enchants will pay for themselves with the time saved while herbing and mining. Remember to continue completing mining and herbalism quests while leveling up to increase the yield of each node making your herbalism and mining leveling experience exponentially more lucrative.
The way Zygor's works is there is an addon called ZygorGuideViewer that is just a UI addition that displays whatever guide you pick (which doesn't have to exclusively be Zygor's Guides). Granted, it offers some other cool capabilities like auto accepting & turning in quests and selling greys, but these are features that other addons can do as well. ZygorGuideViewer works within the bounds of LUA, which makes the addon itself (and therefore its use) "legal".
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.
Blood Elves and Dwarves gain access to Heritage armor as part of 8.1, as well, without a prolonged quest line, though they’ll need to be exalted through Silvermoon and Ironforge, respectively, in order to receive it. A Warfront called The Battle for Darkshore focuses on the struggle between Night Elves and the Forsaken. During the Warfront, you’ll be able to transform your character with temporary abilities, and when your faction controls either the Darkshore or Arathi Highlands, you’ll gain access to world quests.
The prepatch for Legion, for example, offered players in-game demon invasions throughout the world of Azeroth, presenting opportunities for new appearances, feats of strength, a pet, a toy, gear that provided a catch up in power for those with alternate characters or who hadn't played in a while and the opportunity to infect other players via an in-game mechanic.
XP Potions: The Elixir of Rapid Mind and Elixir of Ancient Knowledge no longer drop. They can be bought on the AH still but are way to expensive for it to be worth it. The Excess Potion of Accelerated learning is available from your garrison quartermaster but only works for level 91 to 99. As of Patch 8.1 you can also buy the 10% XP Potion Draught of Ten Lands.