Find the people who specialise in areas the most (e.g. Hugo Giraudel for Sass, Rachel Andrew for grid, Ana Tudor for math, Sara Soueidan for SVG, Paul Lewis for rendering performance, Rachel Nabors for animation, Lea Verou for basically everything else).
Take things apart. Seen something cool/intriguing? Take it apart and then put it back together, but better. Learn by (un)doing.