Today im gonna give you a "Wall-of-text guide" on how to increase your chances to get you the FoS achievement -
Or if you are really setting your goal for it, maybe even get you it!
Disclaimer: This is not for noobs, you must be very experienced with your class, World of Warcraft, fast leveling in general, and you must have the time! This will not work if you are not ready at LAUNCH time, you can not excpect to get realm first if you go to sleep early and then go to school before starting the journey to 90!
Preparing for MoP Realm First:
Things you will need :
#1 Reliable network
You must be 100% sure that you have your network ready for the launch day. One Disconnect and you risk your realm first achievement right there!
Having 1000ms won't help you very much aswell, make sure you have closed every download / porn sites / YouTube or whatever that might cause you to lagg more than wanted.
#2 Food, Energy (Drinks / bars etc)
Even tho you are going for realm first, you need to stay hydrated and not starve. This is pretty self explanitory but you cant spend 30 minutes at level 87 cooking food because you get hungry. What I like to do is to make some awesome taco before launch and eat me full and then wrap some more so I can eat whenever I get hungry, just put it in the microwave for one minute when you have any idle* time on WoW.
*Idle time is a time where there is some cinematic. You probably remember the first time you went to Vasj'ir and had to sit on the boat for 3 minutes doing nothing. This is a good time to go to the bathroom and get your food heated up in the microwave.
Originally Posted by Parrky 
Here's some proper advice, make sure you're preordered and preloaded the expansion and get to bed at a time that ensures you'll wake up near midnight of launch.
Give yourself two hours to fully wake up, prepare your breakfast, lunch and dinner plus any snacks and drinks. Here are my personal recommendations:
Breakfast: Something with a high amount of fibre, my favourite is museli - weetabix is also popular along with shreddies and porridge oats. Fibre does two things, it slows the processing of carbohydrates and makes them a more efficient long term energy provider and it also fills you up. Whatever you do do not miss breakfast.
Lunch: Something along the lines of a chicken sandwich would be great, pasta is another option here but I'm saving that for my dinner.
Dinner: Pasta (with chicken cuz chicken is darn tasty)! Can be served cold and is still tasty!
Snacks: Fruit is good, yoghurt can help digestion and anything sugary is a no no.
Drinks: Water, water and more water. If you're feeling tired after a while, DO NOT DRINK ANYTHING WITH CAFFEINE. I can't stress this enough, caffeine will have you taking pissbreaks every 5 minutes. If you're feeling tired, take a glucose tablet or some sugary sweets like Haribo and energy bars are fine too.
One final piece of advice, take heed of your mortality. You are only human, make sure you rest appropriately when you need it.#3 Privacy
Tell your wife / friends / your dog or whoever you may live with, what you are doing. You dont want your girlfriend charging into your room dragging you to shopping or your boyfriend begging you for le sexy time. So make sure they know, you don't want ANY downtime!
#4 Have the client downloaded!
Make sure you have downloaded the game before the launch! Open the launcher and it will start download (They have allready made the game available for download)
#5 (Optional) Some good music!
What I like to do when playing games is to turn on my kick ass surround sound system and fire up some awesome music! This makes the gametime more fun and less boring
Spotify is a great way to setup music for your gameplay, just make an account on Download Spotify - Spotify (I highly reccomend getting premium so you wont have any commercials between the music which is really annoying trust me.) Make your playlist and put it as "Available Offline" so it wont use any uneccesarry net.
In-game Preperations :
#1 Keybindings
Make sure you have keybindings for targetting and interracting with friendly NPCs, this will make it much easier if there are alot of people blocking the quest givers etc.
#2 Addons
You dont want to spend alot of time clicking accept and and complete and all that, Turn In lets you skip all that and makes you a couple of seconds ahead. Turn In - Quests & Leveling
You dont wanna stop for 10 second figuring out where to go looking at you map. Mapster gives you the ability to have the map open while running around questing. Mapster - Map & Minimap
Make sure all your addons WORK on the Beta, you don't want your addons to crash your client while playing the game.
#3 Daily Quests
Make sure you have 25 daily quests and preferrably normal quests besides that.
I will have the comment below reserved for full guide on all the quests you can get and deliver when MoP hits.
#4 85 Heirloom gear *Note: this is not tested, but it worked at Cata launch!
In Cataclysm only 2 new heirlooms was implemented, the head and the cloak (80-85) Im 99% sure this will work in MoP. Basically since its 80-85 it means you can use it in 85 aswell to gain more exp untill level 86.
#5 Flasks / Potions / Food and inventory
This is pretty much self-explanitory. Clear your bags of trash, put useless stuff in your bank and buy alot of potions, flasks and buff food.
The more buffs you have, the faster you will level!
Beta preperations :
If you don't have beta access, buy it from someone on the forums, get it from a friend, just make sure you have it! If you don't...well then you could pretty much give up allready.
#1 Talents and gear
Figure out the best possible spec you can have. Get BiS gear, the better gear you have, the more damage you will do and the faster you will level up.
#2 Read up on your class
MMO-Champion - World of Warcraft News and Raiding Strategies
Mmo champion have all the updates on every class, I won't teach you how to play, so go read up on that site if you are not 100% sure of what changes gonna hit in MoP and how you will handle that.
#3 90s everywhere!
Go to Battle.net -> Summary -> WoW Beta -> Beta Character Copy -> and copy your char.
Now what? Level it up, level it up 10 times, level it up 100 times. Level it up enough times so you are 100% sure your method is the fastest!
Ask other 90s their /played time and if they did it faster then you? Well guess what, level your char more!
Optimizing your strategies :
#1 Figure out the fastest way to travel
Where should you put your HS? Figure out the best times to change zones. There are many items in-game that lets you teleport to different places around Azeroth!
#2 Enchants and Gems
Keep enchants and gems in your inventory to enchant your new gear. Every oppertunity to gain more dps is an oppertunity to level faster!
#3 Don't kill uneccesarry stuff!
Don't stay around to finish that 1 extra mob you pulled after completing the neccesarry stuff for your quest! Are you a rogue? Vanish. Are you a hunter? Feign Death. Are you a druid? Dash away. Effectivity ftw!
#4 Practice!
Don't stop with the Beta playing until you are fully satisfied with the speed and effincency of your leveling method and you are sure you will get Realm First with that exacy method!
Bonus:
MONKS ONLY!
If you plan on getting realm first level 90 Monk, you HAVE to do the RAF to get your monk to level 81 ASAP!
Basically, grant your monk levels until you hit 79! This is very important, do NOT grant to 80. When you have 99% exp in 79, then you grant the last level to 80. And after you have granted that last level. You will be level 80 and have 99% exp for level 81
Notes : Make sure you are not in a raid group or you will not be able to complete the quests!
Proffession Daily Quests
#1 Jewelcrafting
The NPCs who offer the Jewelcrafting dailies are:
Stormwind :
Isabel Jones - NPC - World of Warcraft
Orgrimmar :
Marith Lazuria - NPC - World of Warcraft
While the quest givers are different, the Jewelcrafting daily quests are the same for both Horde and Alliance:
#1 A Present for Lila - Quest - World of Warcraft
Cut three Timeless Nightstone - Item - World of Warcraft.
This is pretty straight forward, get 3 Nightstones from the Auction House and cut them into Timeless Nightstones.
If you buy the Timeless Nightstones off the Auction House it will not count as the quest clearly states that you need to "Cut" 3 Timeless Nightstones
#2 Elemental Goo - Quest - World of Warcraft
Collect 10 Elemental Goo - Item - World of Warcraft
Portals in both Stormwind and Orgrimmar offer easy access:
Scalding Rock Elemental - NPC - World of Warcraft - Mount Hyjal - Right outside the Nordrassil Inn.