Wow, nice apple. But you are using that photo there right? i think you could get much more improvement and learning using life studies, like taking a real apple, placing it in your desk and painting it. You may use a controled light source or just use daylight
Hmm, nice clouds too, is good to try those things, but try to think of those as subjects with actual form, just like an apple, clouds can be rounded, spherical, box like, and is that whaet gives them form and different shades.