Rule 0: Answer the question
If you're not answering the question then you're wasting your own time and others. Everything you do in an answer should be in support of this goal.
Most answers tend to fall into three categories Yes, because..., No, because..., and Let me explain this concept to you... Start with a short answer to the summarized version of the question.
Rule 1: Sell your answer
Now that you've "answered the question" you need to write to convince people that your answer is correct. Add more information, and explore nuances brought up in the full question's text. All the extra detail should be in support of thesis of the answer.
Answers should be formatted in a way that is simple to read. Don't have a wall of unformatted text. Similarly don't distract from the text by overformatting it. Avoid pictures if at all possible. 487
They look nice but they break up the text and make it harder for people to understand your point.
Rule 2: Have fun
You aren't paid to do this. At the end of the day you're competing for arbitrary internet points. If you find yourself arguing in the comments or getting frustrated, step back, take a deep breath, and go and do something fun. If you're not enjoying yourself it's going to show in your answers.
If you can add a bit of levity, do so, but only if it doesn't detract from the readability of the answer. It's very frustrating reading through walls of text that ultimately have nothing to do with the question being asked.
Some sites allow challenges to the premise of the question in which case your answer will be of the form Don't do x, because... The same basic rules apply but it selling the answer becomes even more critical since you need to defend why you are breaking breaking Rule 0.
Frame challenges are hard to do correctly. At a minimum they need to explain why the expected answers to the question won't meet the actual needs of the OP. Ideally they should also address the actual needs of the OP. 897