Bringing up your character's reputation rating with a variety of factions became more important with the release of the Burning Crusade expansion, and it's set for a more thorough implementation when the next expansion is released later this year. Many people that want to increase their faction end up doing it in an inefficient way, resulting in massive amounts of wasted time. There are certain ways to improve faction in the fastest way possible, but it's not often intuitive to the new player.

If you want to improve a certain Burning Crusade faction, it's best to hold off doing any quests for that faction until you get to at least honored. The easiest way to do this is either to kill monsters in the world in a group that give out the faction that you're trying to raise - or going through an instance that is linked to that faction. For example, if you want to raise reputation with Honor Hold or Thrallmar in Hellfire Peninsula, you should run Shattered Halls, Ramparts and Blood Furnace until you get to at least honored.

This is because you stop gaining faction in most instances (on normal mode) once you reach honored. To improve your faction after that, you'll have to either run those instances in heroic or complete quests for that faction. This allows you to get the big boost from quests after it would otherwise be harder to gain it if you take the time to wait. Deferring your faction gain makes it so that you can get to exalted in faster time.