This is a solid set of recommendations from Nick Gard that will help you keep your CSS in order and in good shape. There’s a lot of rules that relate to accessibility, others to consistency, and some just to simple maintainability, but all are good to at least consider.
After years of writing and maintaining a couple of very large web projects and numerous smaller ones, I have developed some heuristics for writing maintainable CSS. I have used BEM, SMACSS, and CSS Modules for naming, though this article is not about naming, per se. (I tend to use a mix of atomic classes and BEM-ish naming.) This article is more about the properties and values I use or avoid.