This page describes the general guidelines for security and privacy on the internet without delving into specific software and technical solutions. See recommended software solutions here.
Using hardware and software solutions that utilize quality e2e encryption.
Using solutions that are time-tested or based on time-tested design.
If you need to use centralized solutions, use an additional layer of encryption over data to prevent it from leaking to/from the centralized infrastructure. When it comes to files or text messaging, you can use archivers that support encryption or PGP (see description in Recommended Software Solutions) (This will not help protect metadata)