Start by finding Drupal 8 modules on Drupal.org in the "download/extend" section" in "modules" and filter by version 8 ( https://drupal.org/project/project_module?f%5B0%5D=&f%5B1%5D=&f%5B2%5D=&f%5B3%5D=drupal_core%3A7234&f%5B4%5D=sm_field_project_type%3Afull&text=&solrsort=iss_project_release_usage+desc&op=Search ). Then search through module issue queue for patches to be tested. Help the module be ported into Drupal 8 by testing, reviewing patch, and providing the maintainer feedback.

Setup a site with the newest version of Drupal 8.  Download and install the Drupal 8 module you found above.  Review all aspects of the patch, and anything else you can think of.  Document any feedback positive or negative on the module page at drupal.org. Post the module page URLs here with your comments for review.