I was riffing off of an idea I saw in a home decor blog, which had a photo of "vintage horse show ribbons in a frame". I saw that, loved it, and took it to the next level.
The frames are a collection of some I had around, some I bought secondhand, a couple i bought new on sale. First I laid out the frames on the floor and started grouping the ribbons. I'm a graphic designer by trade so it kind of comes naturally, but I basically chose one "important" ribbon to feature in each grouping and then built around that.
After I had my groups roughly figured out, I used duct tape (of all things) to mount the ribbons to the FRONT of the glass in the frame. I might go back later and use hot glue or something to reinforce things. You can't be afraid to overlap--that's what adds the interest. I put some of the uglier/less important ribbons underneath. The tails of the ribbons are wrapped under the glass, sandwiched in between the glass and cardboard backing (where a picture would normally go). I didn't want to cut them, in case I decide to take them out of the frames or rearrange them someday.