The only time I can get great reflective beach shots is during winter. As you know,we get a lot of rain during the winter. Sometimes we get a break in between these storm systems & the sun shines. It has to be low tide as well near sunset. All that rain drains from the land to the beach.With it being low tide,there are these large flat areas.The water coats these areas & makes a fantastic reflective surface!
Having some cool clouds always helps as well!