The Rebbe's guidance on refining one's character traits (middos) — humility, speech, jealousy and more:
Refining character is central. Refining one's character is central to life's purpose; study and memorize Tanya chapter 32 and learn about Ahavas Yisrael (IK 3004). Improving character traits comes with the guidance of a mashpia and by diverting the mind from negative thoughts toward Torah (IK 7490); davening slowly with reflection on Chassidus refines the middos (IK 2931). Personal refinement builds day by day, as in the counting of the Omer (IK 6229), and tzedakah elevates the character traits (IK 8595). True refinement comes from inner discipline, not from mortifying the body (IK 1673).
Humility. Every kindness from G-d should make a person more humble (IK 3268). True humility and self-nullification are keys to awe of G-d (IK 2298), and studying Chassidus before davening fosters humility and joy (IK 3197). Spiritual growth requires making oneself like a desert — open to receive (IK 7661). But humility must be genuine and fit the situation (IK 10800): false humility must not stop one from fulfilling one's mission (IK 6112), a leader needs both humility and inner strength (IK 761, 4487), and healthy pride in the Torah's greatness differs from personal arrogance (IK 4650). Publicizing Torah achievements can be right despite the value of humility (IK 5126). Don't rely only on your own judgment — consult others (IK 3390, 9598).
Speech. Avoid lashon hara, even when it is true (IK 1173, 8231). Speaking negatively about oneself is also forbidden, and it has real effects (IK 1658, 2056, 3795, 4108). Correct others with sensitivity and love, not public rebuke (IK 7172).
Jealousy. Jealousy is usually a negative trait, but directed toward Torah study it becomes healthy motivation (IK 2974, 6658).
See also: Emotional well-being – Anger, resentment and hurt feelings; Personal growth – The yetzer hara and the inner struggle.