I believe there are a few different ways to do it. If your invite can be folded, I would place everything inside with text facing out. They should be able to view the text right away when they open it.

If your invite is a single card, then you can place the cards on top in this order; reception card, response envelope with the response card on top, and then any other information that you may have goes on top of this. When you are done then you should stuff them so they see the information right away.

Hope that helps!