The art of the study.

The artist's study is one of those cherished entryways into the working methods and mental states of the craftsman doing them. Some seek them out from others they admire as one would a cipher to a code that could unlock secrets of lost technique. Studies also tend to have a charm to them in a way not always found in the finished works. The sketch has in its own right become an art form in itself, where once artists did them to gain a better understanding of the subject they were about to paint, artists now have taken away from the subject and turned the object of the studies into the primary focus.

I would argue that some of Ingres studies are better
than his finished paintings.

I don't see the point in this, but I do see the purpose of doing studies in preparation for a painting, there's really no end to the amount you can make before starting one. Here are a few key points I keep in mind when doing my studies:

Trying to get a feel for the likeness of the
main character, Edward Norton.

There's no place for worry; It's a study, you can't forget that. A study is for you, not your facebook friends, or a competition, or other painters perceptions on what something should be. I've never been able to paint well when there were worries on my mind. You have to freely attack the study, see what comes so you can build off of what you discover.

Experiment; Any inclination you might have, any chance of a 'what if,' or 'why not,' you should indulge. Try things in a study that you would never try in a more serious work because you simply never know what can come from it. Instead of copying someone else's technique, experimenting allows you to develop your own solutions to the problems you are about to face. Develop your own voice, just copying technique is trying to fit your message into another painters tune.

Stop and start and stop and start and...; It's a study, you have no obligation to it other than what it can do for you, but think about it like this, in every other art form, the artists tirelessly practice in order to get ready for the end performance, or final draft. Your final painting is the opening night of a play, would you dream of going into it cold? A dancer spends months preparing their bodies so that when the task comes to delivering the performance, they don't need to think about the specific movements, just the expression of the movements inside the harmony of the music. If you want your final painting to be as good as it can be, you must prepare. 

Portrait study of my beautiful girlfriend. Getting the
feel of flesh tone in the light I want, and the various
colors of  stone that will be in the painting.

Educate yourself; I'm sure I'm not the only painter who thinks back on their past pictures and wonders how much better it would be if I had to paint it again. I try to get into the mentality of the object, I ask myself why it feels a certain way when I look at it, what kind of impression gives it its substance. I try to gain that insight when doing my studies.

What is the purpose of this? This is the most important question I ask myself when painting. Everything you put into a picture can either add or take away from the narrative. Is what I'm adding helping or hurting the work? What is its relationship to everything else? A multitude of questions come to me from asking what the purpose is of the object I'm putting into the painting. This helps me stay critical of myself. There's a fine line in a work of art between having a good idea firmly developed, versus a number of good ideas all competing for attention, and never fully realized because one is competing with another. It's easy to lose harmony and cohesion by indulging every whim. 

The more I paint, the more I see the need to get as many of the obviously stupid mistakes out of the way, make room for the more clever, stupid mistakes. The things that end up giving me a hard time are never what I expect.