Dormant ties are the people we used to know. Think about the people you have lost touch with: a colleague from your first job, a college roommate, a client you used to work a lot with, a university professor supporting your research, etc.
Dormant ties can be more valuable than your current relationships. They offer novel information: in the years since you last communicated, they will have connected with new people and gathered new knowledge. In addition, the history and shared experience make it faster and more comfortable to reconnect, and you can count on them to care more about you than your acquaintances do.
Put it into action by leveraging LinkedIn. Sort by your oldest connections or the date of your last exchange. Make sure that people you reconnect with are currently in a situation relevant to yours.
Start by sending a quick LinkedIn InMail message asking them how they are and mention something specific you once had in common. For those who respond favourably, invite them to a quick 15 minute phone call to catch up.
Add a repeating reminder to your calendar for the rest of the month: reconnect with at least one dormant tie each week!
