From Facebook Developer Wiki

[edit] What is a Feed Story?

• A Feed story describes a single specific action between an actor and an object. Examples:
  • "Peter joined the cause Leukemia and Lymphoma Society."
  • "Ari posted a song to Serkan's profile."
  • "Peter thanked Ronnie for his donation."
• A Feed story contains valuable information that the actor wants to share and others want to consume.
• A Feed story is well-designed, succinct, and if appropriate, features an attached piece of media that further describes the action or the object of the action. Examples:
  • "Peter joined the cause Leukemia and Lymphoma Society."
  • "<Leukemia and Lymphoma Society Logo> <blurb about the society>"

[edit] Design Guidelines

• Feed story body:
  • Shows more details about the action or object.
  • Does not repeat information in the headline.
  • Does not include promotional links or explicit calls to action.
  • Example: "<Leukemia and Lymphoma Society Logo> <blurb about the society>"
• Action Links:
  • Appear on all stories
  • Feature contextually relevant calls to action
  • Only one action link with a max of 25 chars can appear in a Feed story
  • Cannot contain any formatting characters (like "[", "]", "|")
  • Example: "Comment - Share - Join Cause"

[edit] Other Guidelines

• Links:
  • All links in Feed stories should go directly to the content without requiring a login (if possible).
• Language
  • Don't use relative time modifiers (e.g., "Peter just won a game of chess.").