The best quality posts meet most (or all!) of the following criteria:
Is relevant, on-topic and adds value to the thread it is posted in.
Is something you put time, effort and thought into and does not appear to be posted with the intent of increasing your post count.
Is easily understood.
Is in legible English with good grammar and punctuation.
Is interesting and encourage more discussion in the thread.
Is not in all caps.
An example of a low-quality post is "good luck", "yes" or "agree" and may be deleted.