My steps in engaging in polite conversation on the internet are:
Explain my point as clearly and concisely as possible.
Try to be respectful of differing opinions and keep an open mind.
Realize that mistakes happen, apologize for my mistakes and admit when I'm wrong. Also, be forgiving of the mistakes of others, point out any mistakes but do so as gently as possible.
Ignore people that are either intentionally misunderstanding you or aren't making an effort to understand you.
I think the first two points are obvious and most people follow them, it's the last two that a lot of people struggle with, even myself at times, but I'm working on it. I think the worst thing you can do on the internet is trash someone's entire idea just because they made one tiny mistake. And putting in effort with trolls will quickly exhaust you, so you need to learn to identify and ignore them.