Sign up for the JoAnn's mailing list. They will snailmail you a add every two weeks that always has a 50% off coupon.
I remember last year I got one with two 50% off coupons in a single add.
To do this you have to go to a JoAnn's store and fill out the card. I'm not sure if you can do it from their site but you can check:
This adds they mail you also have a 40% off online store coupon as well.
But these coupons aren't good for everything. No sewing machines and sale items.