What medium are you using ?
From what I can tell from these pics is you're also drawing way too small to learn much when it comes to values, what size are you drawing on ?
Also, quit using references off the computer to do value studies, set up a lamp and a real sphere and draw that.
Values,shadows, and shading all require a basic understanding of perspective to do accurately. work on your perspective a little bit as well.
So my tip is.. draw from real still lifes, draw bigger, learn some perspective.
Most libraries have books on how to do anything , so look into that as well.
~"With a little hope, and alot of try, anything is possible."~
~"The harder You work, the better life gets."~
~"The pain doesn't last, but the gain will last forever."~
~"Fear is my courage." ~Mr_S_14