I'd recommend just trying to draw the rock in the center and focusing on that. 1. block out basic geometric shapes. You don't have to follow exactly what's in the picture, but it should have a similar feel 2. figure out where the light source is (in this case its from the from the right and is pointing towards the viewer) 3. take those basic blocked out geometric shapes (should be very much like cubes), and the light source, and apply tone. try restricting yourself to 3 tonal values (light, medium, dark).

Personally, I think you have the process of laying down values and tone which is sweet! But i think you should try to squint when looking at the reference photo to really define where the areas of dark and light should go in your piece and try to outline them a little more, this will show what planes are facing the light and which are not. In the reference photo, the image gets much lighter as it moves towards the horizon and the sea is not as dark as it is in your drawing. Hope that helps! :)