Kindness falls under the virtue category of Humanity. Humanity describes strengths that manifest in caring relationships with others. These strengths are interpersonal and are mostly relevant in one-on-one relationships.
Kind individuals believe that others are worthy of attention and affirmation for their own sake as human beings, not out of s sense of duty or principle. There are three traits of altruistic personalities:
Perform a random act of kindness each day (ex: slowing to allow a car in front of you, complimenting a co-worker, buying a treat for your partner, etc.)
Say kinder and softer words to people when interacting through email, writing letters, talking on phone. Smile when answering the phone and sound happy to hear from the person on the other end of the line.
Take out a friend(s) on a surprise dinner and pay for it.