In addition to the programming language or theoretical concepts. It is also essential to develop good problem solving skills.

Concepts like design patterns and refactoring would be better taught using hands on exercises based on a long running example, such as having the students create a project in an introductory course on a programming language and then take that codebase as a starting point for the assignments on design patterns and refactoring.

It would be unrealistic to assume that developers would be working only on a single programming language in their entire career. So, a few pointers on how to go about learning new languages based on similarities with programming language(s) they already know would also be there.