Glad you asked...
You can make a great king's crown with some card stock paper or even construction paper, some jewels, a knife, and glue. If you don't think you can free form a crown, you can print out crown templates. More instructions including templates are found here: http://play.powerhousemuseum.com/makedo/...
Then again, this answer might help you...
An easy way to make a crown is to take a piece of yellow construction paper in half using very large zigzags. Then tape each side with the points up. You can size it to your head and draw diamonds on it if you wanted.

