I use SILICONE-100% silicone aquarium sealant (I got it at Petco -$10.00 for 3oz., a little goes a long way). Anyway, I just fold the ribbon in half and squeeze a thin bead about 3inches from the middle on both sides (does this make sense?) then I spread it out with a popsicle stick. It dries pretty quickly and works super great! I got these instructions from one of the free bow instruction web sites. It's the one with the pink gerber daisy on it, GRRRRR, I can't think of the name of it.
Oh, I cut my ribbon 30" because I do like a longer tail hanging and I've only made them for myself (not for sale yet). I wanted to see how they worked on my weird shaped head and very thick hair. So far, I LOVE THEM!!! I have to say that they are my personal favorites.