Permissions

Set up more than one Owner for each Team (include team’s manager if possible). It is important that Team members know who the Owners are for the Teams they use for collaboration, as well as where to go for support and questions. Team Owners are able to renew expiring Teams.
Conduct periodic reviews of Owners and Members, ensuring that user access is still relevant.

Organizing Teams and Channels

Try to avoid creating different Teams that have the same set of members.
To organize content within an existing Team, it is recommended to use Channels as opposed to creating a new Team. You can organize channels any way that makes sense for you - by subject, discipline, or project.
If there is a new focus or special interest group, add a Channel under the Team that owns this function. The only reason to make this a separate Team is if the content needs to be accessed by different group of users.
Use the General Channel to share an overview of what the Team wants to achieve and other high-level information that a new Team member would find useful. The General Channel is a great place to pin a project charter or a welcome deck to your project.
When naming Channels, remember that the channels will be ordered alphabetically after the General Channel.
Be descriptive when naming Channels to make it easier to understand what the conversation in the Channel is there to achieve.

Keep the data only as long as needed. All redundant, outdated, and trivial ("ROT") content should be deleted.
Store your personal files in OneDrive for Business, and store your group's files in Teams or another shared space.