Spray with water until slightly damp, pinch up the sides in three places. Clip with some binder clips and let dry.
Decorate with cockades, feathers, ribbon...whatever you like. (Thanks to American Duchess for the tutorial on making cockades :-)
Take a few stitches with some heavy duty thread to tack the sides to the crown of the hat for extra strength. I glued seam binding around the edges of mine, but you could also sew it on if your machine can take it or if you want to do it by hand...And there you have it!
Meself wearing said hat... ;-)