On March 23, 2018, Zygor Guides announced that they would end support for their ESO guide. Later, via answers given on the forums, they confirmed they would not add a leveling guide for Summerset. Their guide is Public Domain with Zygor's blessing for the community to create guides. So I took it upon myself to create a Summerset guide for the ESO community.
Blizzard also has a great New Player’s Guide, split into four major sections, as well as its “A Return to World of Warcraft” compendium. And be sure to check out Blizzard’s online forums, especially the New Player Help and Guides forum, where you’ll be able to find more information, ask questions, and engage with some of the World of Warcraft community’s most helpful members.
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.

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Let’s start with the basics. At its core, World of Warcraft is a saga that centers on two warring factions: the aforementioned Horde and Alliance. They’ve been fighting each other since the days of MS-DOS, locked a never-ending war—save for those rare moments where they attempt to team up to counter a greater threat—that has taken them across continents, into space, and through time.
For reference, my previous best time abusing Method-0 in 7.3.5 was 32.4 hours(as show in the old thread). A difference of just over 8 hours; which isn't all that bad, all things considered. And I believe I made several errors along the way, which could be cleaned up in future runs. I believe that that gap could be significantly closed by using a monk's bonus, but I hate playing monk...so...yeah. YMMV
While leveling, try to make use of the new Battle of Azeroth experience gem, Insightful Rubellite, which gives you +5% experience. Equipping one of these requires a socket in your gear, so try to hold on to a piece of Legion gear with a socket or acquire one of the Legion Legendary rings since every class has one. Each of the rings includes a socket. You can acquire one of these rings rather easily by doing World Quests in Legion zones and acquiring 1,000 Wakening Essences that can be used to purchase a legendary ring in the Legion version of Dalaran.
If you love running old content for transmog items, you'll love the new legacy loot system. Whenever a player enters a dungeon or raid where they are 10 or more levels above the content, the dungeon or raid bosses drop an amount of loot equivalent to what would have dropped for a full group when the content was current. That means players could earn loot for five people in dungeons and loot for 20 people after soloing a raid. The legacy loot system also drops other gear types, like cloth dropping for a plate wearer. It's now much easier to get the transmog gear you want, and you can also collect gear for your alts on the same run. 

No matter your experience level—whether you’re about to experience the thrill of hearing the Stormwind City theme as you walk through its epic gates for the first time, or whether you can spell Ahn’Qiraj off the top of your head—here are some tips and suggestions for making the most of your new life in the World of Warcraft (or your epic, Illidan-like return to Azeroth.)
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.
Set sail for the previously unmapped isles of Azeroth. Battle in groups of three as you race against cunning rival intruders—or enemy players—to collect the island’s resources. Constantly evolving challenges await as you traverse frozen landscapes near Northrend, open the mysterious gates of an abandoned Gilnean castle, navigate a war between elementals and more.
The WF/TF system complicates gearing a bit, as you could get an Uncommon quest reward that forges to Epic quality (not a myth - it happened to me on the first night of release). This means that the old ‘Best in Slot' system is, to all intents and purposes, useless, and you should generally opt for whatever item you have that is the highest level - especially as tier gear no longer exists.

Another thing that disappointed me was how Zygor artificially separated their Pet & Mount, Titles Reputations & Macros from the Achievement & Profession guide to inflate their prices. This angered a lot of their existing customers like myself.  Those guides should have been included with the Achievement guide because things like Pets, Mounts, Titles and Reputation involve completing a lot of achievements.
As for the classes themselves, they almost all play like slower and slightly less interesting versions of their Legion counterparts. This is thanks in large part to the loss of one ability from each class that came along with Legion’s own AP dumping system: the artifact weapon, which added a unique ability to every spec in the game. The loss of these abilities left most classes feeling frustrating and incomplete, and though Azerite gear was supposed to be the replacement, it missed the mark completely. There will always be one Azerite trait that reigns supreme for each spec, meaning that the frustration of that particular loop will be unavoidable as long as the system is in the game.
Azerite equipment is currently balanced around being able to unlock the outermost, earliest tier of power immediately upon acquisition, while delaying further advancement until the Heart has been further empowered. For example, the first piece of Azerite equipment, gained shortly after the Heart itself, is fully empowered once the Heart of Azeroth has reached level 3. A character at 120 (the maximum for the expansion) may find a piece whose first tier requires the Heart to have grown to level 12 or greater.
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.

You earn a large rested experience bonus when you log out in this rest areas. This gives you a massive 200-percent bonus to experience gain from most actions (though experience from quests isn’t included). The amount of rested experience you earn increases the longer you’re logged off, and your experience bar will be blue (instead of purple) while you have the bonus.
-Island Expeditions- Island expeditions was one of the new features I was looking forward to but Blizzard no longer makes games that are ready when they are ready but rather makes games ready when the deadline comes. Thus, many of the new features are completely stripped down from what was expected and it's literally just a small scenario you enter with two other players to continue to grind out your Azerite neck piece.
I do not recommend going for TBC, although I remember Hellfire peninsula to be decent, everything else is rather slow. Instead go for WotLK, Borean Thundra gets you levelled very fast, and then you can head straight for Icecrown at 67, which is also insanely fast, although admittedly has a few elite quests. You can go to Sholazar Basin alternatively. 2 zones should get you 60-80 no problem.
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