Denim is really heavy, only 1 layer might be just the ticket! I agree, a 3/4" seam is what I do, if you are only doing 1 layer, you want to be sure you get a good rag.
If you want to do a more conventional rag on down the road, here a couple of good tutorials:
http://greenappleorchard.blogspot.co...-tutorial.html
http://www.lovetosew.com/ragquilt.htm