This page is a travel guide to WoW.
First of all, it should be mentioned that if you want to reach some point on the map while you are still a low level, and the way is too dangerous, a good option is to have a mage portal you to the capital cities of your faction or Shattrath. Alternatively, a warlock can use Ritual of Summoning with two other players to bring you almost anywhere. Either should get you closer to where you want to go.
If you are able to get a portal or a summons to Shattrath, you should consider binding your hearthstone at one of the inns there permanently. Free portals are available to each factions' capital cities near the center of this city, which can save you a lot of time and money later.
Any Alliance mage level 40 or higher should have the portal spells for Ironforge, Stormwind and Exodar. However, the portal to Darnassus is only available to mages level 50 or higher.
Horde Mages get the portals to Undercity, Orgrimmar and Silvermoon at level 40, and Thunder Bluff at level 50.
All Mages can learn the Shattrath portal spell at level 65.
All Warlocks can learn Ritual of Summoning at level 20.
You should be prepared to give the mage some coin. Each portal consumes a Rune of Portals, which costs 20s each, although it is generally considered common courtesy to include a tip for the mage's trouble. As with all player characters, mages vary in temperament and helpfulness, although 2-3 gold is usually sufficient to buy a portal from any mage. Warlocks need a Soul Shard and two party members present (with the Warlock), to perform a summons so they don't commonly perform one unless you are already in their party or in their guild.
Of course these methods can cost money and you're unable to collect flight paths on the way. Still, if you simply want to reach Stormwind as a level 6 night elf, just because all your friends are one of the three other races, and you want to level together, they're the fastest ways.