Hanging Art

Mike and I finally got around to having all of the prints framed that we've been collecting over the last few years.  We used pictureframes.com which I highly recommend.  The quality is great and they are a fraction of the cost of having them professionally framed.  Now we are dealing with the challenge of hanging the art.  We have sort of been fumbling through it....we have a lot of large empty walls in our house which makes it even more challenging because the options are endless.  I found this diagram online which has been a very helpful guide and I've been using my 'art and display' pinboard for inspiration and ideas.  Anyone have any tips for hanging art work?