Details are VERY important when painting or drawing within Photoshop as you will see in the following image. Another way to grab a viewers attention is to over exaggerate details or facial features in Self Portraits.  Over exaggeration can almost be applied to any piece whether it be pertaining to body attributes (boobs, noses, ears) or just surrounding objects and structures (buildings, pigeons, people).

Always consider an art pieces composition! The way you layout the piece can really effect the mood of a drawing, sketch, or painting from total isolation to complete crowded chaos!  Ideally you should have some clearly thought out straight forward underlying meaning to this piece. Just as you would in literature.

Here, I created a little sketch doodle like page to display what I am talking about.