This tip is too easy, but I never thought of it. I always wrapped mine in duct tape. My sewing machine instructor said that she puts her old ones in an empty medicine container, keeps it in the drawer till full then tosses. I love this idea. I don't like to throw mine in the trash where someone might get hurt on it, or some little animal might get it caught in their mouth.
Source: my sewing machine instructor
I also put used razor blades wrapped in a paper towel and secured with tape in an empty prescription bottle. Did this after I had stepped on a razor blade.