Mobile First / Flexbox

Hi! At this point organization of my CSS is quite messy. I wish to hear/see some of your approaches, like: "text declarations first, then margins and paddings" or your favorite way to write comments. At the moment they're very general. I am aware of BEM and SASS and that's the next topics I'm going to dive into. Of course, I'm more than happy to receive some feedback from you. THX for your time. Lukasz