1) This reputation grind is fairly simple and fast. First, fly to Zangarmarsh. Submerge in the center of a structure on a map and you will see an underwater pipe. It leads to several instance entrances.
Once you exit water, you will find yourself in an underground cave and will be facing the raid entrance. There are also three dungeons around it (one to the right of it and two to the left.
2) The fastest way to grind this reputation is repeatedly farming trash in one of three dungeons. Any will work fine, so you are free to choose the dungeon, but the Steamvault (first to the left of the raid entrance) is definitely the easiest to navigate. You want to run it on Heroic difficulty, as that doubles reputation gains compared to Normal difficulty, but make sure to not kill any bosses. After slaughtering all trash mobs in the dungeon, leave it and reset all instances, after which you can repeat the process. If you did kill a boss on heroic difficulty and thus now are unable to fully reset the instance, you can pick another nearby dungeon to farm or return the next day.
If you complete each run faster than 6 minutes, you might hit the lockout limit. I.e. you will not be able to zone in again after 10 consecutive runs (there is an hourly limit of instances entered in wow). In that case, you will have to wait a few minutes, so that an hour passes since your first entrance. However, while waiting you are allowed to enter a new kind of instance, so you can run another dungeon in the bog and return to your preferred one after.
3) Once you reach exalted, travel to Fedryen Swiftspear to buy the mount.
Extra Tips: Humans receive 10% extra reputation from all sources due to their racial buff. Additionally, countless reputation buffs can be utilized to speed up your reputation gains further, such as the Darkmoon Faire Buff (DMF is around for one week every month), WOW Anniversary buff or other mini-holiday related buffs such as Hollow’s End one.
To quickly teleport out of the dungeon and reset it, abilities like druids’ Dreamwalk or monks’ Zen Pilgrimage can be used. Second cast of the ability will return you to the entrance of the dungeon (don’t forget to reset it before reentering). Alternatively, creating a group in the lfg tool and consecutive leaving of the group (without delisting it from the lfg) will trigger a mechanic teleporting you out of the instance after a one minute countdown.