Changes to configuration are how servers break.
BEFORE EDITING
Copy the file first. A dated copy alongside the original costs nothing and is your way back.
CHOOSING AN EDITOR
nano is simple and adequate. Controls are shown at the bottom of the screen. vim is powerful and has a steep learning curve. If you do not already know it, use nano.
AFTER EDITING
Test the configuration before restarting. Apache, Nginx and most services offer a syntax check command. Run it.
A syntax error in a web server configuration means the service will not start, and your site stays down until you fix it.
THEN RELOAD
Reload rather than restart where possible.
THE HABIT THAT SAVES YOU
Edit, test, reload, verify the site works. Every time. Skipping the test is how a one-character typo takes a site offline for an hour.
KEEP A RECORD
Note what you changed and why, somewhere other than the server. Six months later you will not remember why a setting is unusual.
VERSION CONTROL
For anything complex, keeping configuration in a repository is worth the setup.
