Get them under version control. I have a git repo with my skills for software development [1]. There is an installer script that symlinks to the skills. Updating the skills on a machine is then just a matter of advancing the git repo. One of the skills comes with some bash scripts, but the rest are effectively just prompts. Putting project specific skills in projects works well.
I make sure they work by understanding every skill, reviewing pull requests, and testing the end product. The result is rarely perfect, so I am constantly tweaking the skills and how I use AI.