The internet has cultivated a unique culture, one with it's own norms and etiquette. While specific services and websites often have their own distinct culture, there are a few general rules of thumb that apply most places. These fundamentals are often called netiquette.
Common, but not universal, cultural norms online can include:
Activities which could be seen as "Spam" should be avoided. These can include unwarranted solicitation of commercial goods, but can also include non-commercial activities, such as sending a large number of messages in quick succession, making nonconstructive posts, or otherwise acting in a way that is seen as detrimental to the community.
Reviving old threadsEdit
Most forms typically look down on or prohibit "reviving" or "necroing" old threads by creating new posts in them.
What counts as an old post depends highly on the specific community, with some considering day old threads to be old news, and others allowing for the posting in threads that are several years old.
Generally, it's OK to post in a thread that has had active commentary recently. If a community has a thread that was started in 2008 and has had active discussion to the present day, it's not reviving that thread, since the thread never "died". However posting in a different thread that was started in 2008 and hasn't seen a post since 2009 would likely be seen as reviving that thread, and a potential breach of netiquitte.