These artworks are made with digital tools...but some base lines apply here like to any other kind of art...
You have to think of a painting like an idea that you have in mind...it stays immaterial until you start to paint it on the surface of your choice...on paper or on canvas or in the magnetic field of the computers hard drive.
As art shouldn't be about the tools used to make it but about the organization of color, line, form, composition, rhythm and the interplay of all these in support of the subject matter or intent of the work itself. These are the basic and well established tenants of visual art and as fundamental to digital art work as to the cave paintings of Lascaux.
THE BETTER YOU LOOK THE MORE YOU SEE