Facebook uses many factors to recommend the right friends for a person. One of the those factors is the common friends between you both.
Work and education information
According to Facebook, work and education information are one of the factors that contribute to the friend suggestion feature.
The networks you are a part of
According to Facebook, the networks you are a part of can help in determining the people who appear on your list of suggested friends.
The phone numbers you have
There are reports that when you get someone’s phone number, Facebook might add them to the list of the people you may know on Facebook.
It does not use location
Many entities accused Facebook of using location based tracking to suggest friends who are somehow near you. Facebook denied that clearly.
Use of the same WiFi network
According to a patent by Facebook, the WiFi network you use often might affect the friend suggestions you see. If you and a person use the same network often then you might see them in the people you may know list.
The people you stalk
According to many reports, Facebook might be suggesting to you the people you stalk often. In such a case, checking someone’s profile over and over can make them appear on your suggested friends list. (See How to tell if someone is stalking you on Facebook?)
Facebook might be using your interests to tell you about the people that might have the same interests as you.
Being tagged with other people
Some people suggest that being tagged with other people in a picture can make them appear on your friend suggestions list. (See Why do people share photos on social networks?)
People who search for you
Some people suggest that the people who search for your or stalk you can be added to your people you may know list.
The friends of the ones you interact with
Some people suggest that Facebook might show you some of the friends of the people you interact with often.
The emails you saved
Some people suggest that Facebook uses saved emails, if given access to them, to suggest potential friends. This happens if one of the programs on your phone saves the emails to the contact list.
Locations were used earlier
Facebook admitted they were using user locations to suggestion common friends but later they said that they stopped doing that.
Apps linked to Facebook
Some people suggest that when you link a specific app to Facebook, you might get friend suggestions from people using that app.
How does Facebook friends suggestion work?
How does Facebook suggest potential friends? How do Facebook friends suggestions work?