How to add peoples to your google+ circles through People suggestions
- Your mutual connections with people on Google products such as Gmail.
- Interaction you’ve had with others on Google products.
- The links you've added to your profile.
- The connected accounts you've linked on your Google Account.
- The people who are in your extended circles.
- Friends on external sites, when those friends have connected their accounts on their Google+ profiles.
You can view all of your suggestions at once by clicking View all.