One single thing at a time
You know, everybody has been saying it for years, that when we design a software in object-oriented way we must focus on one single thing at a time.
Baby steps. It means setting small, reasonable goals; one tiny step at a time. It's one of the most important best practices for software development.
And we know that most of the good programming principles come back from the 90's. Yesterday at last I connected two items in my memory and recalled exactly where it came from! It was 1991, indeed.