Studies is a really useful thing to maintain as an artist, here I've done a study of an eye to try and gain a sense of realism and try to correctly establish details, including the iris, tear duct, lights, reflections, moisture, fluids, texture.
Anthony Jones (who you can also find listed in my 'Friends and Artists' sidebar) goes on about another way in doing studies.
This kind of came by accident whilst experimenting with portraiture painting, I guess 'Inner Beauty' could work as the there, perhaps...
These are a few illustrations been doing, some commissions and others personal work but all where fun to paint and experiment with.