The question of is it easier to suggest three dimensions on man-made or natural objects is a hard one, man made objects typically have precise structures, perfect angles and if portrayed incorrectly will look very much off to the viewer, but with that in mind the structure of a cube for example when drawn correctly lends itself very easily to be seen as a form in 3d space. There are many variables to consider but I would say overall that the man made objects generally are easier to portray as 3d.
I tried to draw___ to make my objects seem solid
Changing an arrangement of a composition would mostly always seem to change the approach to a drawing. The focal point will change and the relationship to the other items will also be altered the eye will be guided and settle on different parts and a different arrangement may also change the detail and the texture of the items.