Take breaks. Unless you're straight up no-lifing it over a weekend or something, this leveling process is going to take ~40 hours. But any time you do need to step away, log out. That tiny little bit of rested exp is insignificant...but you never know when something might come up and you'll have to leave for a longer period of time than you expected. Better to be logged out and safe(especially with War Mode on) than AFK waiting for a d/c. Plus, you'll need to stretch, eat, shower, and maybe sleep. XD
Any decently geared 90 can complete a Pit of Saron trash mob run in 3-5 minutes. Each mob in the heroic version has a chance of dropping a Battered Hilt, which sell on the auction house for around 10k. Video guides will show the best route to take to pull all the trash mobs at once if you're a class with good AOE; other classes can simply pull less mobs at a time and loot as they go. While this method is a little less reliable than farming Vale-- after all, you're left to the mercy of RNG gods-- it has a higher chance of huge windfall because you could get a multiple hilts every run. Pull the mobs, burn 'em down, and cross your fingers when you loot. On top of the hilts, there's plenty of vendor trash, BoP epics for enchanters, and even a trinket that turns you into a gorilla. You will have to have completed the Forge of Souls in Icecrown Citadel to access this particular dungeon, though.
In recent weeks, players have been giving Blizzard an earful concerning experience gains and leveling in World of Warcraft. It looks like a couple of issues are at the heart of these problems, including time to kill certain baddies and the time it takes to level up between levels 60 and 80. While Blizzard is still trying to figure out why some baddies are taking too long to kill, the hope is that a hotfix launched this week will address the problem of leveling.
_{For the 2nd week of BFA, M+, Raids, and Rated PvP are still not open so there isn’t that much that you have to do. Do your Island Expos to level up your Heart of Azeroth, do WQs for rewards, do Warfronts and the 11 weekly quest turn ins, and run your Mythic Dungeons again to try to get the most gear before reset. I personally will be spending a lot of Week 2 farming mats for consumables for M+ and Raids but whatever you choose to do is up to you.}
Grinding mobs is tedious and slow. Questing is much faster since you get the massive quest experience in addition to the monster's experience. There is no grinding in this guide - you can go through every single level by simply questing! There is minimal traveling time as the guide leads you visually through maps so you can quickly rack up quest experience.
Something to keep in mind as well is that this will make enchanting materials more valuable, since it is likely most players will now simply scrap their boe greens instead of getting them disenchanted. Also redundant dungeon/raid gear can be scrapped rather than traded to the (guild) enchanter in the run. Less stuff gets disenchanted, meaning there will be less ecnhanting materials, meaning their value will rise. All the more reason to DE rather than scrap as an ecnhanter.