How did you improve your CSS skills?

Hello Everyone,

If you ask me, CSS is always a mess. At least that's how I feel about it.

My level of CSS knowledge is decent, and I can do with it what I want. I use Less and sometimes Sass. I consider myself as a junior + on it. However, I am looking for some resources. How can I make my CSS look clean? Where can I put my media queries? How to build your CSS correctly?

Any suggestions?