Gibb's rules are a series of rules by which Mark Harmon's character Leroy Jethro Gibbs governs himself and his team on the NCIS show. There are many rules, with typically only one rule, if any, being revealed per episode.
Gibbs' first rule is "Never let suspects stay together," although a different first rule is later given: "Never screw over your partner." The second rule is "Always wear gloves at a crime scene." The third rule is first given as "Don't believe what you're told. Double check," but is later given as "Never be unreachable." Gibb's fourth rule is "The best way to keep a secret? Keep it to yourself. Second best? Tell one other person, if you must. There is no third best." His fifth rule is "You don't waste good."
Gibbs' sixth rule is "Never apologize. Its a sign of weakness." The seventh rule is "Always be specific when you lie." The eighth rule is "Never take anything for granted," and the ninth rule is "Never go anywhere without a knife." The tenth rule is "Never get personally involved on a case," and the related rule 11 is "When the job is done, walk away." Rule 12 is " Never date a coworker" and 13 is "Never, ever involve a lawyer."
Gibbs has many more rules, and more are added with every season of the show.