formatting - How do I avoid writing text walls in the first place?

I've recently asked a question about editing away text walls once I've already made the mistake of creating one, but it would probably be best not to have them in the first place. What writing techniques should I use to avoid creating text walls when writing long answers in response to written questions?

Ideally, whatever I do will interfere minimally with the ability to generate content; if it's more work than just writing a text-wall-filled post and editing it afterwards it's probably not a good solution.