I have found an excellent web site that explains how to avoid being labeled as a "troll," how to avoid "flame wars" and how to write posts with clarity and courtesy. Here are the links:

Internet Trolls

Flame Wars

Internet Writing Guide - It is a 10-minute course that can help new Internet users write better messages and email.

This series of articles by Timothy Campbell are brief, well-written, and very informative - particularly for the new poster.