First and foremost, be faithful to your superiors, keep all promises, refuse the friendship of all who are not like you; and if you have made a mistake, do not be afraid of admitting the fact and amending your ways.
There are three friendships which are advantageous, and three which are injurious. Friendship with the upright; friendship with the sincere; and friendship with the man of much observation: these are advantageous. Friendship with the man of specious airs; friendship with the insinuatingly soft; and friendship with the glib-tongued: these are injurious.
Friendship with the upright, with the truthful and with the well informed is beneficial. Friendship with those who flatter, with those who are meek and who compromise with principles, and with those who talk cleverly is harmful.
When we have intelligence resulting from sincerity, this condition is to be ascribed to nature; when we have sincerity resulting from intelligence, this condition is to be ascribed to instruction. But given the sincerity, and there shall be the intelligence; given the intelligence, and there shall be the sincerity.