3 column card component using SCSS

Hello everyone, I've just started learning css preprocessors and picked scss, so it's my first project using it. It may be not that good and maintainable as it could be, but writing in scss is really new and unusual thing for me) If you also use Scss, what are the best practises? I'm mean code organisation. And in what situations it is the best to use templates, mixins, math and other things?