Facebook uses algorithms to determine which friends to show you in various parts of the site and apps. The main factors that influence which friends you see are:
How active you are with certain friends
Facebook prioritizes friends you interact with the most. If you frequently like, comment on, or view the posts of certain friends, you’re more likely to see updates from those friends at the top of your News Feed.
Friends you are less active with may have their posts shown lower down in your feed.
Facebook tracks all your interactions – who you view profiles of, whose posts you stop to read, who you message, etc. Friends you engage with the most will be deemed your “close friends” and given top priority in your feed.
How recently you’ve interacted with friends
In addition to overall activity levels, Facebook also looks at recency.
If you haven’t liked your cousin’s posts in 6 months but have been actively chatting with your college buddy, you’ll probably see more of your college friend right now.
Facebook wants to show you updates most relevant to your current relationships and interests.
Interacting with certain friends after a period of inactivity signals those friends are relevant again.
Keywords and interests
The content your friends post also plays a role in whether Facebook surfaces it. If you frequently engage with posts about cooking, posts from friends with cooking-related updates will be shown higher up.
Facebook looks at things like keywords, hashtags, etc. to find overlaps with your interests.
Friends who share more niche interests with you are likely to be shown over friends who post generic life updates less relevant to your hobbies and interests.
How many mutual friends you have
Having more friends in common with someone makes Facebook consider them more important to you. Updates from friends who also know many of your other connections tend to be higher priority.
If you went to the same college or have lots of hometown friends in common, Facebook assumes you share context and want to see each other’s posts more often.
Importance of recent life events
Major life events like marriages, births, deaths, new jobs, etc. also cause friends to appear more frequently.
Facebook recognizes these are meaningful times you likely want to connect with certain people about.
If your close friend just had a baby, got engaged, etc. you may notice their updates appear more for a period after that event as Facebook facilitates social support.
How direct your ties are to certain friends
In addition to activity levels, Facebook also looks at the nature of your direct connections.
A best friend from high school might be a higher priority than your cousin’s roommate you’ve met once.
Things like whether you’re directly friends vs. friends of friends, how you met someone, having recent posts or photos together, etc. help Facebook infer who your inner circle is.
How often you access Facebook
How frequently you log into Facebook also affects what you see. If you use Facebook constantly, the algorithm shows you newer posts more quickly from a wider range of friends.
If you access Facebook infrequently, it tries to show you the best updates from the interim period since you last logged on, focusing on closer friends.
Paid promotions
Facebook allows friends, pages, and advertisers to pay to boost the reach of their posts.
Paid promotions make posts appear higher in News Feeds, even if you don’t interact with the source frequently.
Pages and friends can spend money to get their updates seen by more people. Facebook discloses paid posts, but they may still appear prominently.
Your own posting activity
If you post frequently, your posts reach a higher percentage of your friends.
When you’re more active on Facebook, it assumes your updates are more interesting.
If you rarely post yourself, your updates have lower organic reach and are more likely to only appear to your closest friends and followers.
In summary, Facebook uses a complex algorithm that evaluates your activity, interests, connections, and more to curate your News Feed and selectively display friends. The goal is to show you the most personally relevant and timely updates from your broad social network.