What is the fastest way to level in Shadowlands 9.1? There are a handful of options you must consider if you are trying to level as fast as possible in 9.1.
Make sure to log out in an Inn or any major city to gain rested XP. While rested XP can get pretty specific in how it works, you will know you are rested if your player portrait glows, and your level circle says "zzz."
Rested XP gives you bonus XP to a certain point, until you spend all of your rested points. You rack up more rested points the longer you stay logged out in any Inn or major city.
Wowpedia has a fantastic entry that breaks down rested XP really well.
Fastest Way to Level in Shadowlands 9.1
Heirlooms are a little different in Shadowlands than they were in the past. Previously, many heirlooms would give a 5% increase in XP gained, and the more heirlooms you had on, the more you could stack this 5% XP buff.
Blizzard has done away with the 5% buff from Heirlooms, instead opting for set bonuses that reduce rested XP consumed. Two heirlooms reduce rested XP consumed by 30%, and six heirlooms will reduce rested XP consumption by an additional 30%.
Once you reach level 30, you can turn on War Mode in your talent window. War Mode will give you a 10-30% XP bonus, depending on your level.
While War Mode is turned on, you are effectively on a PvP server, and can be slain by any member of the opposite faction, so long as you are out of any starting zone. War Mode should most definitely be thrown on once you hit level 30, as other players shouldn't slow you down as fast as the 10-30% XP bonus ends up helping.
The Darkmoon Faire is a once a month event that can provide players with a couple buffs that increase XP greatly.
Riding the carousel for a measly amount of coins will give you the "Whee!" buff, which grants the player 10% bonus XP for an hour. The Darkmoon Top Hat when worn will give you a 10% bonus XP buff, but only while the Darkmoon Faire is in town.
These buffs are handy, but the time spent to go out the way into the Darkmoon Faire is generally not worth the trade-off most of the time. If you have a batch of a ton of quests, say 15+, then it may be worth it to head to the Darkmoon Faire and grab both the Whee and Hat buff, but even then the time spent is debatable.
Join a Guild!
Lastly, while not an outright buff in XP gained, joining a guild can help speed up the leveling process greatly.
Since the Cataclysm expansion, Guild Perks have existed. Guild Perks are bonuses a Guild bestows on any member of the Guild, whether you are the founder or just joined a second ago. The two Guild Perks that are most useful are Mount Up and Hasty Hearth.
Mount Up increases speed while mounted by 10%, and Hasty Hearth reduces the cooldown of your Hearthstone by 15 minutes, making the cooldown 15 minutes instead of 30 minutes.