How do you debug a broken or non-functioning cron job?

Run either crontab -e, crontab -l, or check /var/spool/cron.

Bonus points if they say to run the script manually, extra super bonus points if they check the crontab for any custom env settings, or run it under cron with all output saved to a file (instead of the default e-mail, which might be broken for other reasons).