I do 1 to 3. So I pour 1 cup ACV to 3 cups of filtered water. I think Chicoro says that in her book, and that's where I got it from. I may need to double check the ratio, but I'm sure that's what I use.
I've been rinsing before I do protein treatments and before I deep condition, because I read that your hair should be stripped of everything before applying the goodies, so that they actually bond to your hair and not to product/build-up. But I am interested in learning/trying to do the rinse after I condition as BrownSkinQT said to see how that works as well.