Occasionally, in my job as an engineer, I write process descriptions of the technology we are selling. Those are part of commercial offers, intended to win the customer. Those are bundled with drawings, technical offers and the like. We are selling complex plants and it is safe to assume that there will be an engineer reading the offer, and maybe other management staff. I write these in German and English. This is not something I do very often, but it crops up.
So far, the procedure has been to take the last document we did that is relevant or similar to the job on hand, and edit or expand it. There's lots of marketing speech in older documents, some of it (I think) is only understandable when one knows the technology. So when I do a session of copy, paste, edit, I change rather a lot.
This answer to another question suggests reading similar documentation and understanding their style. This seems to be good advice, but only partly doable because the exact style of documents I write is one that I hardly get (I write offers for plants and read offers for components).
Now, I'd like to have a few best practices or guides to follow when doing this, because I want to arrive at a consistent style that actually conveys what we are trying to say.