I’m not sure there is a vast rulebook you’d find useful. Generally, when I manage to follow my own advice, it pays to stick to the following:
(a) Be polite and reasonable, no matter how utterly repellent the other position is. I’ve been caught out before by jumping down someone’s throat after misinterpreting what they’ve said, and I’ve regretted it.
(b) Read, re-read and re-read again every post. Stop to wonder if there’s a different interpretation to what you’ve just read. If you’re not sure, ask for clarification from the poster. I’ve seen nasty little spats over that kind of thing plenty of times.
©. Cites. Inevitable, really. A point backed up by authoritative evidence is generally far worthier of consideration. Of course, the quality of that evidence depends on many factors. When posting evidence, I try to pick sources that are either generally accepted as authoritative, appear to have a large amount of expertise in that area, or at the very least are as politically neutral as possible. An anti-abortion website may have absolutely correct statistics and opinion poll results, but you may find it difficult to convince someone taking the opposite viewpoint that it’s a credible source. Ditto with party politics.
(d) If you’re relying on personal anecodotal evidence and opinion, state that clearly. There’s nothing wrong with a debate stemming from opinions, but remember that your opinion is no more ‘correct’ than anyone else’s.
(e) Prepare to learn and to change your mind. If you’re so utterly convinced about something that you won’t even entertain the possibility that you could learn something new that might alter your opinion, why bother participating at all?
(f) Avoid common logical fallacies. This one still intimidates me, but I see the point. Certain arguments should not receive the same consideration as others if they rely on ‘underhand’ tactics. For example, the straw man misrepresentation of someone’s position, or attacking the person rather than their position. I know there are more formal logical rules around debating, and I’m sure there are many posters who can provide more on this, but these are the ones I try to follow.
(g) Everyone makes mistakes – be ready to acknowledge and apologise if you get snappy, or have misread a post, or if your position/evidence is proved to be suspect. That’s just me; I don’t like conflict.