When you are previewing groups in Student Preview, don't forget to add your preview student to a group, or else you will not be able to see any of the group items

Don't limit your students to only using Blackboard for their group communications, allow them to choose a medium they will actually use (e.g. instagram, MS Teams, What's App, etc.)

Create your groups before you create the assignment.

When you create your group assignment, select which groups will be assigned that assignment. You have the option to create different assignments to assign to different groups.