Writing consistent and readable CSS that will scale well is a challenging process. Especially when the style sheets are getting larger, more complex, and harder to maintain. I have created this set of rules to simplify decision making and maintainability when developing new projects. The following rules assume we are using CSS preprocesser like SASS (.scss) to simplify our lives.
As a general rule of thumb, code should be as modular as possible. Don't be afraid to break CSS into seperate files where it makes sense.