You asked, “How do I begin choosing LinkedIn groups?”
LinkedIn groups provide a forum for those interested in a specific topic to share information and learn from each other. You can join an existing group or create your own group for a specific purpose. I created the “CyberLife Tutors Connectors” LinkedIn Group to share information on networking and jobs.
The owner of the group determines if the group is open to everyone or has restricted access requiring approval of the group manager. The group owner can pre approve or invite others to join the group.
Search in the group directory on a subject of interest to you. Review the search results to select groups to join. I read the description of the group and note the number of members. A useful national group or global group will have thousands of members. Groups bound to a geographic area might have hundreds of members.
You can choose up to 50 groups to join. Have fun!