Similar to how Google’s PageRank sorts results to better match your search intention, Facebook uses Edgerank to ensure that engagement is optimized and spam is minimized. BrianSolis explains the underlying EdgeRank factors that define whether or not someone sees a post in the news feed.
1) Facebook looks at whether or not you’ve previously interacted with an author’s posts or whether or not your friends are engaging around those posts.
2) If content is or isn’t engaged by your social graph and the network at large affects what you see and what you don’t see.
3) EdgeRank also examines whether or not your have interacted with similar types of posts in the past, i.e. photos, videos, polls, etc.
4) If content or page hosts have received complaints by other users, chances are that you will not see it.
Read more details and how to improve EdgeRank at BrianSolis.