Add a Changelog (best named 'Changes') to the distribution. It should list at least major changes implemented in newer versions.
Add a META.yml to the distribution. Your buildtool should be able to autogenerate it.
Add a README to the distribution. It should contain a quick description of your module and how to install it.
List all used modules in META.yml requires
Add a META.json to the distribution. Your buildtool should be able to autogenerate it.
Add tests or move tests.pl to the t/ directory!
Define the license if you are using in Build.PL. If you are using MakeMaker (Makefile.PL) you should upgrade to ExtUtils::MakeMaker version 6.31.
Add 'use warnings' (or its equivalents) to all modules (this will require perl > 5.6), or convince us that your favorite module is well-known enough and people can easily see the modules warn when something bad happens.
This is not a critical issue. Currently mainly informative for the CPANTS authors. It might be removed later.