Get the right colour
Take pictures of the beach you want to model in the weather you wish to model it and mix Humbrol enamels to achieve the right shade. Add more white the closer you get to the beach as the sea gets shallower.
Get the ripples right
Whereas a beach gets walked on and has undulations all over, the waves go from the sea to the beach. Make sure your waves are in gentle curves and varnish the sea, achieving a glisten as the light hits the water.
Aquarium filter wool is great for creating waves and breakers. Cut a thin strip and work varnish into the wool helping it stick to the water. Rough up some wool where the sea hits the rocks to make a splashing effect.
Make realistic breaks
With swimmers in the water, carefully arrange the wool around them to give the impression that the water has been disturbed by them being there. Cut the legs off some of the swimmers so they appear partially under the surface.
Get the Gear
The aquarium filter wool is available from eBay for less than £10 and will comfortably cover a small beach. Two rolls may be required to cover large areas but spare wool can always be used wherever steam is necessary.