If you're anything like me, you don't just have one sewing machine with a single cord. It can never be that simple. There's the serger, iron, and whatever other small appliances you need for your particular sewing project. And all those cords get in the way and tangle in the knees when I'm sewing. It's very irritating and quite easy to solve.
I picked up a couple 2" magnetic bulldog clips at the local office supply store. I do a lot of shopping for my sewing supplies over there. These clips just about saved my life. I use them to secure the many cords to the underside of the sewing table. Of course, you need a metal table (or metal on the table) for this to work. Once clipped, the cords are kept away from my legs while I'm working, don't tangle with themselves, and are not in the way. Therefore, I don't trip on them as I move around the room, and my children and dogs don't get tangled and pull a heavy sewing machine or iron down on top of themselves.