One thing that I have learned that many seem to not be able to do is to live life by the mantra "it is better to be happy than to be right." This works for any relationship whether it is friendship or marriage.
Don't sweat the small stuff. If you think you are right about something but know that an argument or worse will happen if you assert your opinion, then you are better off just not saying anything and keeping the peace. In the grand scheme of things, the only thing that matters is your happiness, not winning a irrelevant argument.