Be mindful of which classes, properties, methods, etc. that you declare as public or protected. There are a lot of things that need to be public (RockWeb needs it, another dll needs it, or a plugin developer would need it), but in many cases internal or private is the better choice and will avoid breaking changes.

Also be aware that code elements marked as internal are still available to be referenced in unit tests or integration tests, because the test projects are given access to the internals of other Rock assemblies using the InternalsVisibleToAttribute.