Avos 3:12

Rabbi Yishmael said to act promptly towards those above us (i.e., be quick to serve them) and kindly towards young people, and to greet everyone cheerfully.

Avos 3:13

Rabbi Akiva said that jesting and levity accustom a person to lewd behavior; the oral tradition is a protective barrier around the Torah, tithes are a protective barrier for wealth, vows are a protective barrier for abstinence, and a protective barrier for wisdom is silence.