A useful thing that some distros have started doing is setting the color of your shell prompt differently if you’re logged in as root. This gives you an additional visual cue that helps avoid doing things as root when you don’t want to. If your distro doesn’t do this for you, you can accomplish it by changing your .bashrc files. To set the color of your shell prompt you set the shell variable PS1.
To make the prompt red when you’re running as root add this to /root/.bashrc:
To make the prompt green when running as a normal user add this to ~/.bashrc:
See the shell man page and search the web for ANSI Escape codes for more info on the meaning of the escape sequences.