During the making of any painting there is an order that usually follows in a logical manner.  For instance tone the canvas, sketch the composition, apply paint-fat over lean.  When I'm toning the canvas that is my focus.  At that moment it is the most important aspect of painting to me.  The same goes for sketching, color mixing, brush strokes, edges....etc.  Whatever I'm working at has full attention (as it should).  However, more and more I find "location" to be my most valued tool in paint application.  Location of the point where the darkest shadow will be, or the corner of the barn, the eye or jaw shadow.  The location from which all references will be made.  "The chief corner stone" ,so to speak, that anchors the rest of the painting.  This is, of course, part of the composing process.  The locating of the objects on the canvas.  I have in the past chosen a "general" area for this or that and ended up moving things a little here or there.  What a waste of time and effort!  If this happens on just one painting it is no big deal.  But multiply by several hundred and you see my problem.  So now I make a special effort to get my first "locating" dot of paint in the correct spot.  You probably already knew that didn't you?  I love it when I think I've learned something.  Best wishes, Jerry