Never, ever involve a lawyer. (Season 6, Episode 7; Gibbs is said to have other rules involving lawyers, but according to Tony, this is the "umbrella" one)

Rule #13

• Permalink: Never, ever involve a lawyer.
• Rating: Unrated

Bend the line, don't break it. (Season 11, Episode 4)

Rule #14

• Permalink: Bend the line, don't break it.
• Rating: Unrated

Always work as a team. (Season 5, Episode 5)

Rule #15

• Permalink: Always work as a team.
• Rating: Unrated

If someone thinks they have the upper-hand, break it. (Season 8, Episode 24)

Rule #16

• Permalink: If someone thinks they have the upper-hand, break it.
• Rating: Unrated

It's better to seek forgiveness than ask permission. (Season 3, Episode 4)

Rule #18

• Permalink: It's better to seek forgiveness than ask permission.
• Rating: Unrated

Never, ever bother Gibbs in interrogation. (Season 4, Episode 10)

Rule #22

• Permalink: Never, ever bother Gibbs in interrogation.
• Rating: Unrated

Never mess with a Marine's coffee if you want to live. (Season 2, Episode 9)

Rule #23

• Permalink: Never mess with a Marine's coffee if you want to live.
• Rating: Unrated

Rule #27: Two ways to follow: First way, they never notice you, Second way, they only notice you. (Season 7, Episode 15)

• Permalink: First way, they never notice you, Second way, they only notice you.
• Rating: Unrated

Always watch the watchers. (Season 8, Episode 22)

Rule #35

• Permalink: Always watch the watchers.
• Rating: Unrated

If feels like you're being played, you probably are. (Season 9, Episode 1)

Rule #36

• Permalink: If feels like you're being played, you probably are.
• Rating: Unrated

Your case, your lead. (Season 6, Episode 16; Season 10, Episode 3)

Rule #38

• Permalink: Your case, your lead.
• Rating: Unrated

There is no such thing as coincidence. (Season 7, Episode 21)

Rule #39

• Permalink: There is no such thing as coincidence.
• Rating: Unrated