Humanity is just learning to communicate in the Net, but the rules of good form here are no different from those that must be observed in the real world. Do not insult others, do not be intrusive, do not let your negative emotions get out of control, write competently.
As in life, on the Net we have to be in different communities, and the rules of communication may differ. A polite person, once in an unfamiliar society, will first of all try to find out its features. Somewhere it is customary to communicate on “you”, and somewhere – on “you”, somewhere emoticons are appropriate, but somewhere – not. There are companies where the use of online slang is encouraged, and there are those where they simply will not understand it or consider you illiterate.