The Rebbe's guidance on anger, resentment and feeling hurt by others:
Overcoming anger. Remembering that G-d is always present and sees everything helps a person overcome anger on the spot, as explained in Tanya (IK 9135, 9795). Regular study and review of specific passages in Tanya and Iggeres HaKodesh on anger — making it a habit — helps uproot it (IK 5588). Pause before you speak (IK 8351). Serve G-d with joy and humility, not with anger or frustration (IK 7874). Anger harms both relationships and business, and self-control, especially over anger, is good for emotional and physical health (IK 1906, 5557, 4985).
Letting go of resentment. Real forgiveness means not only refraining from retaliation but removing all resentment from one's heart (IK 7451). Hold no grudges; dedicate your abilities to the good of the community instead (IK 2083). Don't let an old grudge keep you from a relative's simcha — trust in Divine Providence and attend (IK 4919). Focus on others' potential rather than on past disagreements (IK 4167).
In the family. Resentment toward a parent's shortcomings is eased by focusing on the sacrifices she made (IK 2954). Avoiding disputes, giving tzedakah and asking forgiveness foster family harmony and help control anger (IK 6670).
Don't blame others. Don't attribute misfortune to someone else's supposed grudge or anger at you; look to G-d, the true source of every blessing (IK 2680).
See also: Teshuvah – Asking and granting forgiveness; Marriage – Shalom bayis.