Quotes must be original -- eg. no quoting someone quoting Mark Twain. When in doubt, Google.
You must credit quotes by linking the LJ post where you found 'em and the username of the quotee. ("Even 'Friends Only' posts?" Yes.)
If you do quote from a locked/private entry, ask for permission. Let us know you got permission by adding "QWP" to your post. Public posts/comments don't need it. Quoting locked posts without permission is a bannable offense.
Mods' Note: Yes, we may delete off-topic, unfunny, or rule-breaking posts, and we may ban users who can't follow the rules or who repeatedly give us grief. However, we may also make exceptions, because this is a fun com and we're nice that way. Also- there's mod posts with stuff maybe not covered here.