Alliance
Stormwind City to Borean Tundra
Go to the Stormwind Harbor in Stormwind City and board the boat on the northernmost dock. If the boat isn’t there, simply wait a few minutes for it to arrive. This boat will take you to Valiance Keep in Borean Tundra, where you can start the Northrend quests.
Menethil Harbor to Howling Fjord
Go to Menethil Harbor in Wetlands and board the boat on the north side of the docks. Make sure you board the boat that looks like a steam boat. If the boat isn’t there, simply wait a few minutes to arrive. This boat will take you to Valgarde, where you can start the Howling Fjord quests.
Horde
Orgrimmar to Borean Tundra
Go to the western zeppelin tower outside of the main entrance to Orgrimmar and board the north zeppelin. If the zeppelin isn’t there, simply wait a few minutes to arrive. This zeppelin will take you to Warsong Hold, where you can start the Borean Tundra quests.
Undercity to Howling Fjord
Go to the smaller zeppelin tower outside of the main entrance to Undercity, which only has one platform, and board the zeppelin. If the zeppelin isn’t there, simply wait a few minutes to arrive. This zeppelin will take you to Vengeance Landing, where you can start the Howling Fjord quests.