Silk neckties make beautiful 3-D embellishments. I often use them along with Clover's yo-yo makers to make silky circles that keep their shape indefinitely. Beads or buttons can be added to the center of smaller yo-yos to add sparkle. There are instructions to be found for fabric flowers that are easy to make. Try some from recycled neckties!
Because a collar is sewn to a curved edge, it can be difficult to fit if the neck edge is not properly prepared. To prepare the neck edge for a collar, you will need to "staystitch". This means sewing about 1/8" inside the seam line of the neck edge as a first step. Then you will clip up to, but not through, the stitching at 3/4" intervals. This allows the neck edge to open up to almost a straight edge that you can easily fit the collar, hood, or other neckline addition.