My second least-favorite part: leveling ranges. Zones are divided into leveling ranges; some are for levels 10-60, others for levels 58-80, and so on. On the surface, that appears to make sense; while there are odd moments where you're presented with the content from two expansions at once, it does mean that you're more or less going through content in order, at least by expansion if not by level.
Like most of those experienced players, I had all the benefits, including a full set of heirloom armor, which helps to boost the experience my character would get (though that bump was reduced at the same time the other changes were made.) I had a guild, the ability to fly in every zone, and pets and toys that made a pile of things more convenient. My new character started at level 20, as all allied races do.

These two expansions are virtually identical in terms of exp/h. I personally favor Mount Hyjal, and think it's very slightly faster. But if you know Jade Forest well you can just as easily keep up there. Ultimately you'll end up doing both anyway, so it's mostly academic. Every time I've tested Valley of Four Winds or Deepholme, or any other zone in MOP/CATA's level range, they were worse exp/h. You should not even need to complete both zones to ding 91, so it's more important to just pick one and go.
Zygor's Leveling and Loremaster guide is the ultimate tool for players who want to level up quickly and earn the coveted Loremaster achievement. This guide will lead you quest by quest through every zone, telling you exactly where you need to go, how to complete objectives, and everything else required to reach level 120 in the fastest time possible.

Do quests and complete the story of your first chosen area before returning to your capital to scrap all of the equipment items you acquired. You should be around Level 113 by the time you complete your first area. Before selecting your second zone, head to your faction hub ship to acquire your introductory quests to the mission table and your champions. Complete this introduction and then pick up the quest to establish your first foothold in enemy territory.

I had multiple people ask me why I didn’t do blood or prot for leveling on DK/Pally and the god honest truth is the fact that I know how to play ret and unholy quite well and the limits of the class. I tried leveling as prot and good Christ it felt like I did no damage. If you take selfless healer and wake of ashes you should have 0 issues with leveling as Ret and it is significantly faster. As for Unholy if you take grip of the dead to kite a little, deathpact for healing, and keep up with your Dark Succor (spelling?) procs you will have no issues. I died once as DK and none as pally. The only classes I struggled with a little was WW and Shaman. WW because the aoe felt under-tuned at the time and shaman because they are trash imho.
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!
Fully rested experience (this is the blue color your experience bar takes instead of purple) grants 200% more experience per kill. Quest experience does not work the same as mob experience. Instead of just using the rested bonus, quest experience pushes the bar further upwards extending the rested bonus. Say if half your experience bar is blue. If you turn in 10 quests all at one the normal experience from them all could boost a character a full level. Unlike mobs where the experience gain will use up said bonus - the quests merely 'push' the bar further. Doing this could net you a level and still have the 200% bonus for mob kills applying to milk the rest bonus.
Enchants. I honestly wasn't 100% certain which enchants were best, since scaling has screwed up a lot of things. IMO, just pick the enchant for each armor slot that has the highest bonus without level restrictions. The exception is that you'll definitely want Mark of the Hidden Satyr for your neck piece, and probably Elemental Force for your weapon. Both of these proc consistently and strongly across all levels.
Even though the value of gold relative to real money plunged during the Legion expansion, we didn’t see corresponding increases in auction house commodity prices, with the exceptions of big-ticket vanity items like TCG mounts. Consumable prices in gold were actually stable or falling during the same period that the value of gold relative to the dollar was plunging by more than 80 percent.
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jame, addon version or your guide is F$%&ING AWESOME, THANK YOU. there is a part in the first section of the guide where im instructed to take shindrell's not to kayneth stillwind, but there is no instruction to pick up that quest on the way through astranaar, if i find anything else like this ill let you know, love your guide, thanks for taking the time to put it together!!

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.