Using the words "Please" and "Thank You" are incredibly important. If you find that you do not use them enough, I encourage you to form the habit. I myself, as polite as I believe I am, must remember to respond with "You're welcome. "
What about our tone of voice?
What we say may go unheard, if our tone suggests rudeness, impatience, anger, disgust and more. Let's practice lowering our voices but speaking clearly and patiently. How we speak to someone can diffuse a volatile situation or prevent one altogether.
Does your body language betray you?
It is said that 90% of all communication is through body language. Are you speaking the right words but folding your arms or tapping your fingers? From personal experience, I can tell you my body reacts when I see a potential negative encounter about to occur. I have tried to train my body to remain in a calm stance when dealing with negative, obnoxious, rude or angry people. How someone acts is usually a reflection on what is going on with them and not you personally. Which brings me to:
Don't take it personally
Many times I have encountered a situation where someone approaches in anger or frustration and my decision to not take it personally has helped tremendously. In fact the kinder I try to be, the more the other person can relax and sometimes even admit they are sorry for their behavior, saying it has nothing to do with me.
Ultimately, we cannot change how others will behave. We can either approach an encounter with kindness and respect or react to bad behavior with our own bad behavior. Difficult people are exactly that, difficult. It is not always easy to maintain a calm demeanor but one can certainly learn how to, especially when you detach your emotions from the situation. If a situation escalates, ask for help. Sometimes all it takes is someone else's perspective to resolve a problematic encounter.
"Be kind whenever possible, it's always possible." ~ Tenzin Gyatso, 14th Dalai Lama