Do not post entire articles that are available elsewhere on the Internet. It is simply unnecessary and can make following the flow of the conversation difficult. Quoting a few paragraphs is better, as is posting a picture – aim to post just enough to give the gist of the article or the point you are trying to make. Provide a link at the end so that the reader can click through to the full content if they so choose. Try to keep the text relevant to the topic as much as possible.