Heirlooms: Heirlooms are the best source of bonus XP for leveling. All slots can be gotten pretty easily now, except the rings. The time you need to spend to get the rings if you haven’t gotten a level 3 shipyard in WoW is way too long, so getting the rings is generally not worth it. Having all your heirloom gear will boost XP by 55%. Generally, you want heirloom gear with crit on for leveling as you want to kill mobs in a few hits as possible
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.
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.
The cloak is nice because you only need one of these instead of the previous cloak versions since the primary stat changes depending on the class it is used on. The on use trinkets for versatility, haste, or critical strike could be very strong if used together by numerous party members with the same trinket. Finally, the threat reducing trinket could be useful for solo levelers in dungeons with newer, non-heirloom geared tanks in order to not pull threat on some larger packs of enemies.
There are also a number of different online tools you can use to make yourself a better World of Warcraft player—and to help you decide what to focus on. Wowhead has a great Attunement Tool that shows you how close you are to unlocking significant milestones in the game, like unlocking new allied races, earning reputations with key factions (which will ultimately help you unlock faster mount speed and other goodies in the game’s expansion), and how far along you are in your dungeons and raids.
Azeroth paid a terrible price to end the apocalyptic march of the Legion’s crusade—but even as the world’s wounds are tended, it is the shattered trust between the Alliance and Horde that may prove hardest to mend. As the fires of war continue to roar, take the battle to both new and familiar lands with the Tides of Vengeance update, and join your allies to champion your faction’s cause.
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.