Select the relevant area and fill it with blue. You can do purple if you like, but a greenish blue is more realistic.
Go to Filters > Noise > Add Noise. Choose Gaussian Monochromatic and set it to about three to five. Then go to Filters > Blur > Motion Blur. Set the angle roughly paralell to the shore (unless there are strong currents or the wind is really choppy or whatever) and the distance pretty low.
Deselect the farthest ocean (hold down Alt to deselect) and repeat with a little more noise and a little farther distance. And again. Do this three times at least - the more often, the more it will look like distance. Now you've got waves.
Next, we make it shiny. Duplicate the layer and name the new one something like Light or Reflection. Reselect the whole ocean. Got to Filters > Sketch > Bas Relief. You want a lot of detail and not too smooth, with the light direction being in the distance. That's probably too strong, so reduce the opacity of the layer a lot.
And another layer (Ctrl-Shift-N) named Highlights. With a small, soft brush, make some white dots or short lines on the ocean. Maybe grow the brush a bit for closer highlights. Add another motion blur.
For sand, add a fourth layer and drag it to the bottom of the pile. Fill it with a somewhat greyish yellow and add noise. Little to no blur is necessary, but if the sand is also far away, you want a very low amount of noise, uniform instead of Gaussian, and not monochromatic.
It's easier to add the foam of waves crashing with the sand layer already in place. Go back to the highlight layer. Select a small, soft brush and reduce its opacity to about fifty. Make a line or two paralell to the shore. Not too clean. I prefer to blur these manually, so hit R and select a large brush. Then return to the original water layer with the burn tool, and shade under some of the waves so they look a little more like they're curling. And that's it.