Some general thoughts based on the types of things I do. (All of these points do not necessarily refer to all answers.)

• If you can add something new to the answers already provided, then do so.
• If your answer only refers to part of the question, state this clearly.
• Check your information against published documentation and cite these sources in your answer.
• Provide example code (and any appropriate output) to support your answer.

I sometimes find that, after researching the answer or trying some test code, I do not have anything useful to add to what's already been presented: in these cases, I have invariably learned something myself.