No rules for me either. If it's something I think will be good for a backing and it's really on sale (CHEAP) I might buy 8 or 9 yards of it. Same for something I can use in my Linus quilts. Also will pick up fat quarters just because they'll blend with something else I have. Make your own rules. If you are concerned about colors, I've seen shoppers with little notebooks that have fabric samples glued into them so they can match colors. Whatever works for you. Just have fun with it. Happy quilting. Glad it was love at first quilt!