shading is an art in its own but once you crack it youve got it for life.
I was actualy using a method today which i like to call hardsoft. Basicaly under sunlight for example, hard shadows are shadow areas created by objects blocking the sun from another object. I tend to do these first and these create excellant sence of depth in your piece. Next you have soft which is created by round objects that gradient the shodow over a surface. In actual fact the shadow is still hard but its hard at such a small scale and over such a relativly large surface that it gives the illusion of blending seemlesly with each shade. The sharper the edge the harder the shadow. Basic things realy that ive made to sound amazing but there realy simple stuff to learn. Using both these styles together should work well. It does for me.