One thing I really liked was using Project Euler. Step 1 for any given problem was to solve it. Step 2 was to go through code written by others benchmark it,

One thing I really liked was using Project Euler. Step 1 for any given problem was to solve it. Step 2 was to go through code written by others benchmark it, and learn why there code was faster than mine. https://projecteuler.net https://projecteuler.net