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.
I'm Adam Roberts, an artistic traveller documenting the world of Art, Design and Travel but you can click my face for more on who I am or you can click below to view my other work