The Proverbs have much to say about how to be a good friend, and chapter 27 has two well know wisdom axioms concerning friendship, consider thoughfully the wisdom of each:
Proverbs 27:17 - As iron sharpens iron,
so one man sharpens another.
Proverbs 27:6 - Wounds from a friend can be trusted,
but an enemy multiplies kisses.
Wisdom Project - 27