There are cases with series where the prequel is written after the story, but is still meant to be read before it, and there are cases where that is NOT so (like star wars. IMO, at least). To those who have already read past this question(as in it is no longer an issue to you) which should I read first, and if it is up in the air, which did YOU read first?

I don't want to ruin any 'suspense' by starting in the wrong place, because this looks very interesting.

I don't know about the author's intent, but I read Dear Green first because it was published first. Most of Dear Green: Hitomi no Ounowa is prequel, but the last few chapters take place after Dear Green, referencing things that happened there.