Artisan: Persons, typically smallfolk, who have specialized in making products such as weapons, pottery, and other items.
Hedge Knight: Wandering knights who are not sworn to a particular person or house.
Godsworn: Members of the clergy of a religion such as Septons or Septas.
Knight: Any person that has been granted knighthood but has common origins.
Maester: Scholars and healers that have completed their training at the Citadel.
Men-at-Arms: Armed soldiers in the Seven Kingdoms of Westeros, usually of common origin.
Merchant: A person who buys and sells goods for a profit, especially commodities from foreign lands. Merchants can be from anywhere in the known world.
Noble: Members of the noble families of Westeros.
Noble Knight: A person that has been granted knighthood and is noble by birth.
Retainer: Persons, typically smallfolk, who work for members of the nobility or royal family as servants such as cooks and stablehands. Those wishing to be a retainer to a noble or royal family can discuss backstory ideas in the same way potential kin might.
Royal Family: Members of the royal family including the King and Queen as well as the princes and princesses.
Sellsword: A soldier who hires out his services to the highest bidder. More common in Essos.
Smallfolk: The common people of Westeros who lack lands or titles that do not fall into subcategories such as artisan, merchant, or retainer. Some examples would be actors, thieves, carriage drivers, and farmers. A more extensive list can be found on the Occupations page.