With the introduction of Drupal 8 the Composer package manager became the goût du jour for me. And once you start using Composer to manage your PHP-projects you never want to do it any other way.
So how do you go about it if you want to spin up a WordPress site using composer? There is plenty of useful information to be found on the internets, not least from the competent people at roots.io. This piece was written all the way back in August of 2013, but still seems to be the best summary out there: