I think the way we can be most kind in the world is to break everything down to the most simplest way. Use common sense, don't be a jerk and don't do things to people that you wouldn't want done to you. Right? Today I am finding that too many people have trouble with the common sense thing.
On a more thoughtful note, I think its important to consider the following when you have the urge to be mean, defensive or aggressive towards someone...that you cannot always know what is going on for a person and sometimes you can only imagine that they could be having the worst day of their life.