I read this recently on Rachelle Gardner's website http://www.rachellegardner.com/ She's a literary agent who posts all kinds of advice, mostly for writers but also other interesting pieces.
Before saying something, use the old method of asking yourself:
Is it true?
Is it kind
Is it necessary?
The post details other ways to be polite and civil in our hectic and sometimes thoughtless society. The kind of things your mother used to tell you. Some of the advice is specific to modern devices, like cell phones and how they are used. It does seem to me though that if we only spoke what was necessary the world would be a much more silent place.
Here's some other thoughts:
People will often fail to live up to your expectations.
People will hold different viewpoints from you.
Try to remember that most people are doing the best they can with what they have, and give them grace.
Sometimes it is useful to step back and remember that most of us prefer to live in a civil society and we all need to do our part. Or maybe embroider one of these sayings on a pillow and consider it daily!