This part of the leveling process will be a lot faster if you pick up a Grimoire of the Four Winds. This item is sold on the Black Market Auction House, so the price will be dependent on which server you play on. With this you can learn to fly in Pandaria at level 85 instead of 90, so the process of leveling up will be a lot faster.
Check out all parts of the leveling guide:
Part 1) Level 1 - 58 / vanilla leveling guide.
Part 2) Level 58 - 70 / The Burning Crusade leveling guide.
Part 3) Level 70 - 80 / Wrath of the Lich King leveling guide.
Part 4) Level 80 - 85 / Cataclysm leveling guide.
Part 5) Level 85 - 90 / Mists of Pandaria leveling guide.
Part 6) Level 90 - 100 / Warlords of Draenor leveling guide.
Part 7) Level 100 - 100 / Legion leveling guide.
Level 85 to 90Head to the Jade Forest once you are level 85, and skip the first invasion quests completely. You can pick up the regular quests in the zone without bothering with these. While doing this, keep staying queued for each dungeon once, and complete all quests tied to the dungeon for a nice experience boost.
The experience points needed to hit 90 is really low, and you will most likely be 90 before ever finishing Jade Forest if you do all the dungeons at least once. This part should not take more than a few hours if you got a flying mount.