Sand the painted frame to distress it to your liking.
Play around with the positioning of your starfish on the frame. The points are different lengths and sometimes bent in or out a bit. You just want to have as many points as possible touching your frame. On this one all but the top point hit the frame. Put a dot of glue where the frame and starfish meet and let dry. I use tacky glue.
As simplistic as this one looks with three floating fingerling starfish; I probably spent an HOUR positioning and repositioning all the various starfish I had in my stash to find just the right ones to fit perfectly in this tall skinny frame!
ALL of the framed shell pictures shown ARE for sell, either in my space at Stars Antique Mall in Portland, Oregon; or in my on-line etsy shop.