A Talmid Chakham must avoid six acts: to go abroad in perfumed garments; to walk alone at night; to wear shabby shoes; to converse with a woman while on the street (even if she is his wife); to sit in the society of an ignoramus; to be the last to enter the beth midrash.
"He who understands astronomy", says Yochanan bar Nafcha, "and does not pursue the study of it, of that man, it is written: 'But they regard not the work of the Lord, neither consider the operation of His hands'" (Isaiah).
Rabbi Yochanan also says that only someone able to answer all Halakhic questions, even those which deal only with the insignificant treatise Kallah, is a Talmid Chakham worthy to be appointed leader of a community.
[6] The principles with which the Talmid Chakham must live are enumerated in the first chapter of the work Derekh Eretz Zutta, opening with the following sentence: "The way of the wise is to be modest, humble, alert, and intelligent; to endure injustice; to make himself beloved of men; to be gracious in his interactions, even with subordinates; to avoid wrong-doing; to judge each man according to his deeds; to act according to the motto, 'I take no pleasure in the good things of this world, seeing that life here below is not my portion.'
Even when he held no official position in the community, he supervised religious activities, determined the time and form of prayers, verified weights and measures, etc.