In addition to the excellent advice above,
WoWWiki has reputation guides for each faction.
Pay particular attention to the repeatable quests or kills which stop providing faction after a certain point, and make sure to get the best benefit from those before advancing to the next Reputation level.
Take the Consortium for example. Prior to patch 2.3 it was very difficult to get Consortium rep to Exalted unless you were very, very careful about what you did and when. There are two repeatable quests which you can't repeat after you become friendly, so do those until you become friendly. And then Mana Tombs runs can take you to Honored. At that point running the standard quests becomes 'economic', as every remaining repeatable quest or Instance run which provides rep continues to do so until Exalted. You can make the best use of your time if you try to run whatever daily Instances they offer in the Lower City, as you'll get some reputation with the Consortium as well as possibly with some other factions, and you'll also start collecting Ethereum Prison Keys, and 5 of those makes for another repeatable turn in for rep and coin.