Looks like that along with choosing your weapon, armor, and magical abilities, you can also choose a path into a guild that comes with related perks.
The ESO guilds are:
The Dark Brotherhood is the guild of Assassins. They get orders from the Night Mother to kill specific targets for a set price. These targets are prayed to the Night Mother from people all over Tamriel.
To get into The Fighters Guild, you must defeat the Daedric Guardians of the Dark Anchors sent by Molag Bai to drag Tamriel into his plane, Coldharbour, to earn the guild's favor.
Fans of the Rift MMO will recall finding books/scrolls all over the place, and for The Mages Guild, that is exactly what you must do, also! Find the Lore Books strewn about, within cities and mines, or hidden in obscure places, to earn favor with this guild.
The Thieves Guild is a group of Thieves that work together for the people. They specialize in sneaking, breaking and entering, and stealing, of course.
As more information becomes available, this post will be updated, with hints and tips and locations for the questlines for each guild.
If you'd like to submit anything to add. please post in this thread.
Overseas until the end of August.