I wish I knew!
I try to write in everyday language, and to avoid technical terms if there’s a simpler alternative. Normally, it doesn’t sound condescending, just conversational.
When it comes to your manifesto, you’re going to have a lot to say, in a very small space. Keep it short. Don’t make people wade through paragraphs of fluff to get to your point – if they’ve got a hundred manifestos to read, they might just not bother with yours.
You can break text up with bullet points and internal headings. You can put key words and phrases in bold text, but have a good look at how that appears on the page – sometimes it works well, and sometimes it looks silly.
I find it helpful to use questions as sub-headings (as you can probably tell!). It is a good way of telling people upfront what the purpose of your paragraph is, and drawing them in to the answer. That might not be a great format for a manifesto – if I remember rightly, it’s been tried before and didn’t go down too well – but it might be helpful for your website.
If you have time, you might want to run your writing past a couple of friends, and ask for their impressions. You don’t have to change everything they suggest – it’s your writing, after all – but it might be helpful to have a sense-check before releasing it into the wild!