The golden rule for kindness is not to be a fair-weather friend. Stick with them in their troubles and help them through it!
Also, try to not get mad. If you do get mad, go somewhere by yourself until you cool off.
Say only thoughtful words! Never say anything rude or unkind about or to a person. Words can be either a potent venom or the antidote. Think before you say them! Only kind words can minister to a mind diseased.
