Chunky white sweater, black leggings and black shoes (can be heels, but no need. Biker boots work just as well). Just make sure the sweater (or shirt beneath) covers your butt. That's simple leggings rules. This outfit is very easy, yet pretty.
I like these boyfriend jeans withe the tennis shoes - but I don't like the patch on the knee. I don't mind a few tears, but don't like the patch. This is a great casual look - including the white top and jacket.