Gather and look through your collection of CDs. Group the covers that have a common theme. Group them by genre (all classical CD covers), color (all red covers) object (covers with a guitar). Or it can be completely random. Hunt through second-hand stores and garage sales for cheap CDs that have interesting covers. Consider how big you want this collage to be and look through antique stores for inexpensive frames. Cut out your own cardboard backing if it is missing.
Cut the first page of the album covers (the page with the picture on it) and throw away the rest of the album booklet. Lay out a plan for your CD cover collage and take a picture of it for future reference while you glue. To thin your glue, add it with a little bit of warm water and carefully blend together.
Apply the glue to the cardboard backing with the paint brush where you want to put the first cover. Pat out air bubbles and streak spots with a lightly dampened washcloth (it should barely be wet) as you glue. Layer your CD covers as much as you want and try to fill in blank gaps. Add the actual CDs to the collage for an interesting effect.
Let the collage dry before applying the first coat of water-based polycrylic. This will protect your project from dirt while adding a finishing sheen; Minwax.com provides professional advice on how to use polycrylic. Wait a few minutes for the first coat to dry before adding a second coat. Attach it your frame and proudly display your art work.