Sparkly Seas and Light

When there's lots of light and just a gentle breeze you get sparkly seas. Smooth seas don't sparkle, angry seas flash and are very white, or if the light's low they're grey, but a gentle breeze creates a sea that is interesting and a joy to paint.

Mary Kemp - Paddling

I usually start with the background colour of the sea, squinting to get the tones right in my head and then add the splashes of sparkle later. Generally bigger sparkles at the front, smaller at the back. Of course this is very simplistic and there's no substitute for observation.