First decide if it's really something worth your time. Then, spend several years playing with the std lib and maybe dabble with Boost. Read stackoverflow thread

First decide if it's really something worth your time. Then, spend several years playing with the std lib and maybe dabble with Boost. Read stackoverflow threads tagged with [c++] sorting by vote count descending. Read the tests in popular github c++ projects. Read A Tour of C++. Most importantly, write and rewrite lots of code, test it, debug it, and try out cool ideas you think of. If you get stuck, context shift to another task where you're not spinning your wheels.