If very angry, an hundred.

In 1825, the year before his death, Thomas Jefferson — the 3rd U.S. President and a Founding Father of the United States of America — was asked by a father to supply some words of wisdom to his young son, Thomas Jefferson Smith, who had recently been named after him. Jefferson graciously responded with a handwritten letter, at the end of which was the following 10-point list of advice for the youngster, titled, "A Decalogue of Canons for observation in practical life."

Each and every word still rings true.

Transcript follows.

Transcript
A Decalogue of Canons for observation in practical life.

1. Never put off till tomorrow what you can do to-day.
2. Never trouble another for what you can do yourself.
3. Never spend your money before you have it.
4. Never buy what you do not want, because it is cheap; it will be dear to you.
5. Pride costs us more than hunger, thirst and cold.
6. We never repent of having eaten too little.
7. Nothing is troublesome that we do willingly.
8. How much pain have cost us the evils which have never happened.
9. Take things always by their smooth handle.
10. When angry, count ten, before you speak; if very angry, an hundred.

(via Lists of Note)