golden rule

from The American Heritage® Dictionary of the English Language, 5th Edition.

• noun The ethical principle that one should behave toward others as one would have others behave toward oneself.
• noun An expression of this principle, especially the words of Jesus in the New Testament verses Matthew 7:12 and Luke 6:31.
• noun A fundamental principle to be followed in order to ensure success in general or in a particular undertaking.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• noun idiomatic A fundamental rule or principle.
• noun ethics The principle that one should treat other people in the manner in which one would want to be treated by them.

from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.

• noun any important rule
• noun a command based on Jesus' words in the Sermon on the Mount