The Western Plaguelands for the Alliance is a great zone and is looked forward to by most players. There are not particulary many quests but the zone introduces you to Scourgestones and most players will begin their grind for faction with the Argent Dawn. This will be similar to the Horde guide and is split up into the three zones; Scourge fields and cauldrons, Andorhal, and Hearthglen.
First of all once you hit 50 and finish the area you were on get the quest A Call to Arms: The Plaguelands (Alliance) from any alliance capital city. Then make your way unless you have the flightpath to Southshore or Aerie Peak to enter the Western Plaguelands from the south. Going further in makes your way to the small alliance outpost of Chillwind Camp. Accept all the available quests and collect the flightpath and you are ready to begin.
(finishing later, correct mistakes if needed)