A good advice is to avoid experimenting with new add-ons on a production site. Most organizations set up a shadow of site of their live server that is used as a sandbox. Once the installation is successful, the procedure is re-applied on the production site.
Additionally, it is recommended that you make a complete site backup before installing any third-party software. That way you can roll back in case of a disaster.
Download an add-on.
Put Moodle in maintenance mode.
Unzip files (either locally or on the server).
Copy files in appropriate location(s).
Start the Moodle admin page to run the installer.
Test the add-on (and remove if it does not work; refer the uninstall section ahead).
Put Moodle out of maintenance mode.
Most add-ons are structured in a similar way. However, some modules either don't follow this standardized approach or require other steps, especially...