We cannot change others; we can only change ourselves. So ask yourself before saying anything "Will what I say make a situation better?" If the answer is no, don't say it. Ask yourself before taking an action "Will this make the world better?" If the answer is no, don't do it. Your motivation when making choices is also important. We can do good things with the wrong motivation and the impact is lessoned in our lives and those of others because the intention was not sincere.
The poet and scientist Johann Wolfgang von Goethe observed that man is a herd animal who does not wish to be part of a herd. Thus, man is forever in conflict with his own nature. And, since he is innately in conflict with himself, it is difficult to deal with him.
"There is no greater love than charity" is, indeed, good advice for one's endeavors with others. Not always being insistent upon having to be the one above all others at something is wise, often, too. Considering others feelings before one's own; having manners is usually a sound way to deal with other people. However, since others often are self-centered and demanding for their desires, it is, indeed, difficult to deal with such people. One teacher always told her classes, "Good manners is no more than considering the feelings of others before acting."
It's hard to do this when we have no idea about how you are dealing with others and in what situations.
Sadly, the only kind of generic advice that is possible (to me) is that you have to have the self-discipline to treat all people the way you would want them to treat you. The hard part there is having the self-discipline.
You'll hear all sorts of techniques, like trying to put yourself in their shoes and trying to understand how your actions will affect them. But what it all comes down to is having the self-discipline to do what you know is right. Sadly, there are no easy ways to achieve that.