Have you ever unfriended someone? Is it acceptable to do so without explanation? The descendants of Emily Post have taken a stand on 21st- century challenges. They rule that it is fine to ignore a friend's request, untag yourself from a photo or skip the quizzes that you are sent by a cousin. And, it is acceptable to unfriend or unfollow someone without explanation.
As for Twitter, they say, do not be a Twitter Bore. Don't tweet about what you had for breakfast. Make sure that your 140 characters are relevant and something that "people really need to know". What you had for breakfast is probably something that no one gives two tweets about.
And, as for form, well, it seems that the rules for good writing apply just as much online as they do to traditional pen and paper. So, take note. And, No all CAPs, please and do not skip punctuation.