“Life is partly what we make it, and partly what it is made by the friends we choose.” -Tennessee Williams
Start by making a list of people you haven’t seen for some time or those whom you miss. Is it an old classmate, a distant friend, someone who has moved away, a relative? Choose one of these people and take steps to reach her/him.
If it helps, think what it would be like for you to hear from someone who has lost touch with you, specifically someone you’d really like to hear from.
Note, any style of communication is fine but you will get more from the exercise if it extends beyond an email or voice mail message to some kind of exchange.