I made a super easy reusable Swiffer cover tonight! Seriously, it took 5 minutes. I normally put a microfiber rag on my Swiffer, but it doesn't stay on very well. So I sewed elastic onto it! I previously tried to crochet a Swiffer cover, but it was too complicated and I gave up. This was really, really easy.
You need a microfiber rag a little bigger than your Swiffer (you can get these at the dollar store). Or, you could use any old rag or towel you have. You also need about 1 foot of 1/4" elastic.
Place your Swiffer on the rag, and trace about 1" around it. Cut out the shape. Zigzag or serge around the edges so it doesn't fray. Then, sew the elastic around the edge, stretching it as tightly as you can. That's it! It's nothing special, but it works great.