When you render the clouds and use the hard mix (or threshold adjustment layer, they give you the same effect if I recall) you will end up with lots of random patterns and such. What I do at that point is to take a black brush (soft round usually 200px) and paint out the areas I want to be ocean then switch flow and opacity to 10 or 20% and go closer to the shoreline - with the softer settings it gives you more opportunity to brush lightly around edges you want to keep without changing too much. Then I switch to white and paint the inside the areas I want to be land.
Don't just trust the random clouds to do what you want them to do, sometimes you need to get in there and muck around a bit, kind of like molding clay - slap it onto the table (rendered clouds) then push it into the shapes you want (brushing)
Oh, and welcome to the guild!