Heaven help you all who start stained glass. It is REALLY addictive. It's not hard to do but you need patience and time. I've tried several ways but my favorite is using black (or color of choice) tape and stitching it on with a twin needle.
I put all my pattern pieces on double sided iron on, cut them out and press them to the backing. Then following the diagram, and the is always one, add my tape. I've had some beautiful results.
So far, I have used purchased tape with 50% coupons but my projects have been no bigger than card table size. I would make my own tape if I did a quilt or large wall hanging. Tape is expensive and getting very hard to find.