Use good libraries and pay attention to what makes them appealing. Large programs should usually be structured as a collection of libraries. When you are design

Use good libraries and pay attention to what makes them appealing. Large programs should usually be structured as a collection of libraries. When you are designing an API for your own libraries, think back to how other libraries solved similar problems at the API level. Many (most?) worthwhile design patterns can then be derived from scratch as a way to achieve a particular API structure.