Here are some ways that can help you ensure your safety in SharePoint. Some of the best practices can be effectively insuring the correct users have the correct permissions.
A systematic guide to effectively set SharePoint permissions can be found here: https://www.lynda.com/SharePoint-tutorials/Plan-Sharepoint-permissions-basics/466190/494716-4.html?autoplay=true
You must log into Lynda.ou.edu first to be able to view the video. These Lynda videos will help you keep your SharePoint site safe. It is recommended that you use group permissions rather than individual permissions so you can keep track of who has what permissions in each group.
Here is also a link to the 365 KB: https://support.office.com/en-us/article/understanding-permission-levels-in-sharepoint-87ecbb0e-6550-491a-8826-c075e4859848