Such a brilliantly simple solution, and I can't even claim it as my own: my friend was helping me decorate my apartment for my birthday party, and as I debated where to drill holes for hooks to hang the garland from, he said, "Why don't we attach it to the studs with magnets?". Why not, indeed!
This works best, of course, with nice lightweight garlands or ribbons, and for me it worked like a dream. We attached the garland to the ceiling at intervals (studs are generally 18-inches apart), draping it nicely. The only hiccup was that I kept forgetting the garland wasn't actually attached to the ceiling, and would tug at it and rearrange it, causing the magnets to fall! That's when it's very helpful to have someone down on the floor who will repeatedly (and non-judgementally) pass the magnets up to the top of the ladder for you. Teamwork!