Hey there!
Immediately I think there's a lot of work to be done in terms of shading on the examples you posted above. Shading is directional and strongly associated with planes of a surface - the way you shaded the cylinders and volumes above is very arbitrary and does not follow proper light/shadow behavior in real objects.
I recommend you do a lot of observation of simple geometric volumes to understand how light is affected by changing planes, THEN move on to trying to cast shadows and interactions between several forms.
It's alright to use references when making these, too!