There are five Ideals. The First Ideal is the motto of the Knights Radiant and was shared by all ten orders. The four later Ideals were said to be different for each order of Radiants.
"Life before death. Strength before weakness. Journey before destination. That was their motto, and was the First Ideal of the Immortal Words. There were four others."
Kaladin raised an eyebrow. "Which were?"
"I don't actually know," Teft said. "But the Immortal Words - these Ideals - guided everything they did. The four later Ideals were said to be different for every order of Radiants. But the First Ideal was the same for each of the ten: Life before death, strength before weakness, journey before destination."
Life before death - The Radiant seeks to defend life, always. He never kills unnecessarily, and never risks his own life for frivolous reasons. Living is harder than dying. The Radiant's duty is to live.
Strength before weakness - All men are weak at some time in their lives. The Radiant protects those who are weak, and uses his strength for others. Strength does not make one capable of rule; it makes one capable of service.*
Journey before destination - There are always several ways to achieve a goal. Failure is preferable to winning through unjust means. Protecting ten innocents is not worth killing one. In the end, all men die. How you lived will be far more important to the Almighty than what you accomplished.
The Second Ideal
I will protect those who cannot protect themselves.
I accept that there will be those I cannot protect!
– A specialized form of the Fourth Ideal of the Windrunners, as sworn by Kaladin
I will cleanse the Shin of their false leaders, so long as Dalinar Kholin agrees.
– A specialized form of the Fourth Ideal of the Skybreakers, as sworn by Szeth
The Fifth Ideal
Called the Ideal of Law, this requires the Skybreaker to swear an oath that they will become a personification of law and truth. Nale is the only current Skybreaker to have achieved it - and the only Herald - as it has been centuries since anyone mastered the Fifth Ideal.
*According to Brandon, there are several sorts of ways that he interprets this, and like all of them, he wants to interpret them differently throughout the books. Rhythm of War digs into "strength before weakness" a little bit more. Like the other two (i.e., "life before death" and "journey before destination") "strength before weakness" has a natural sort of sense to it. We are strong and everyone will be weak. And the idea is that one is strong for the weak when the weak cannot be strong, because someone will need to be there for the other to be strong when one is weak. Everybody is weak sometimes; everybody is strong sometimes, and we need each other. That's kind of the philosophy behind "strength before weakness."
It has been theorized by fans that the "most important words", in King Gavilar's message to Dalinar, given with his last breath:
Brother ... You must find the most important words a man can say.
... were a reference to the Immortal Words and Gavilar's way to set his brother on the path he would take for the rest of the novel.