Once you have established the sky and water within a beach drawing, the sand part of a beach scene is quite simple to draw. Essentially, you will lightly shade in the foreground from the edge of the water, which will naturally define the space as sand. You can add little ripples into the sand by drawing a set of lines parallel with one another in the same formation. You can play around with adding ripples and lines into the sand to establish how uniform or disrupted you would like the sand to seem. Otherwise, if it exists within the context of an image with a sky and ocean, it will naturally be contextualized as a beach or sand. You can also shade in the entire sanction and use your eraser to create lines, which can be a cool way to establish highlights within the sand.