Never let suspects stay together.

Never screw over your partner.

Don't believe what you're told. Double check.

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.

You don't waste good.

Never say "you're sorry." It's a sign of weakness.

Always be specific when you lie.

Never take anything for granted.

Never go anywhere without a knife.

Never get personally involved in a case.

When the job is done, walk away.

Never date a co-worker.

Never, ever involve a lawyer.

Always work as a team.

If someone thinks they have the upper hand, break it.

It's better to seek forgiveness than ask permission.

Never, ever bother Gibbs in interrogation.

Never mess with a Marine's coffee... if you want to live.

There are two ways to follow someone. First way, they never notice you. Second way, they only notice you.

Always watch the watchers.

If you feel like you are being played, you probably are.

Your case, your lead.

There is no such thing as coincidence.

If it seems someone is out to get you, they are.

Never accept an apology from some someone who just sucker punched you.

First things first, hide the women and children.

Clean up the mess that you make. Also stated as, "Never leave behind loose ends."

Sometimes - you're wrong.

Never trust a woman who doesn't trust her man.