I've made several rag quilts and love them. I think the easiest way is to sew an X on each block. That holds the batting down best IMO. If you aren't careful how you quilt the squares the batting can roll up between the layers. Oh my ..... when you wash them and dry them to get the raggedy look make sure you clean your washer and dryer lint trap out!!
Have fun with it and be sure and post a picture of the finished quilt. :D