Wrap it with Twine. You can decorate mason jars in endless ways but these twine ones make stunning centerpieces. Here is the DIY mason jar twine, but feel free to adapt it to add lace, doilies, even chalkboard paper
Buy rectangular vases, fake flowers, rocks, ribbon, and candles the width of the rectangle. Glue the flowers to the rocks and fill with water. Float the candle up top. Glue the ribbon around the top of the vase.