My son wants to grass dance, so im also looking for some more ideads on how to sew the yarn on. So glad i saw this thread. But I've done projects where i had to sew ribbon fringe onto some shawls and something for my son. This is what i did, and it worked great for me.
*measured out what i needed for the project for each side (for each side, and the bottom)
*cut out all the ribbon twice as long as i needed it and melted the ends alittle.
*then laid down a piece of masking tape sticky side up for as long as i needed it for the the part i needed it on, taping down the ends of tape so it stayed on the table.
*the i would fold the ribbon so the middle came to an upside down V (so theres only one layer of ribbon on that part of of the tape).press it on the masking tape.
*when i had all the ribbon in the design that i wanted i would tape down the other side, sandwiching the ribbon in the middle.
* sew it on to where its needed.
I dont know if this is the "right" way of putting ribbon on, but ive tried hand tieing it, but that took way to long for me, and i like the way it looked sewed on better... buts just me. Hope that helped. Good luck, and i was really glad to see the other ways of doing this too.