This is a guide where I will try to explain what you can do to level up most efficiently when it comes to gear, buffs and other misc stuff. This is not step by step leveling guide, but I will you what you can use to level up most efficiently. This does not include RaF.
Items overview:
Heirloom Chests - 10% additional exp from level 1-80.
Heirloom Shoulders - 10% additional exp from level 1-80.
Heirloom Ring - 5% additional exp from level 1-80.
Heirloom Cloaks - 5% additional exp from level 1-85.
Heirloom Helms - 10% additional exp from level 1-85.
Heirloom Legs - 10% additional exp from level 1-85.
Elixir of Ancient Knowledge - 300% additional exp for one hour. Works from level 1-84. DOES NOT PERSIST THROUGH DEATH.
Heirloom Trinkets - No additional exp, but effects scale with level. From level 1-80
Heirloom Weapons - No additional exp, but scales with level. From level 1-80
Misc BoA Weapons: - Obtained from Archeology and found in various locations in Pandaria.
Misc Boa Armor: - Obtained mainly from Archeology
High iLvl 409 Weapons: - High iLvl BoE's usable at level 80. (This gear is equivilant to level 85 Dragon Soul gear). Hits like a truck.
High iLvl 409-417 Armor: - High Ilvl BoE's usable at level 80. (This gear is equivilant to level 85 Dragon Soul gear).
High iLvl 450 Weapons: - High iLvl BoE's usable at level 85. (This gear is equivilant to level 90 blues.) Hits like a truck.
High iLvl 450 Armor: - High iLvl BoE's usable at level 85. (This gear is equivilant to level 90 blues.)
Note: There are various high iLvl BoE's between 81-84 and 86-89 as well, but I decided not to include that in this guide. (You can use the WoWhead filters for that.)
Misc:
At level 65, make sure you do the [Ring of Blood] quest chain in Nagrand for a lot of exp in short time.
At level 75, make sure you do the [The Champion of Anguish] quest chain in Zul'Drak for a lot of exp in a short time.
At level 75 you can use [Adventurer's Journal] for a chance to get a 10% more exp buff that lasts an hour.
At level 84, make sure you do the [The Crucible of Carnage] quest chain in Twilight Highlands for a lot of exp in a short time.
Join a level 6 guild or higher for additional 10% exp from [Fast Track].
During Hallow's end, go either to Undercity or Stormwind and get [Grim Visage] or [Unburdened] which gives you 10% more exp/rep and lasts 2 hours. DOES NOT persist through death, but you can pick it up again. If I level through dungeons or PvP I usually camp where the buff is grabbed.