In addition to soaking up as much knowledge as I can about CSS architecture, I’ve spent a ton of time recently learning more about front-end performance.
Harry Roberts excellently rounds up and explains here in detail a lot of the strategies I’ve picked up over the last few months, plus a few more. He covers markup structure, parallelisation, prefetching, gzipping and minifying, among other things.
Definitely a must read for anyone diving into this topic.