Drawing for the Absolute and Utter Beginner Paperback - 2003

Excerpt

As you add values to your sketches, they will gain a sense of dimension and weight. They may look less like fleeting impressions and more like solid objects, especially at a distance. The more time you spend adding visual information to your drawing, the closer you get to creating a study. The name itself implies that the artist has spent time closely observing the object. This scrutiny may result in more substantial, solid-looking drawings, with more detail and refined technique. The major differences between sketch and study are that in creating a study, more time is spent at a slower pace, adding a greater amount of detail, with more refined value application

Take Your Time
Many beginners wonder if they're taking too long. It's not how long you take; it's how long the drawing takes. Just stay with it until it feels and looks finished-- to you. 
If your sketches are developing into studies, or you'd like them to, add the following points to your drawing approach. For creating a study:
-Slow your pace.
-Break up contour lines into smaller overlapping lines.
-Keep your pencil in closer contact with the paper surface.
-Fill in values with greater precision.
-Add more detail.
-Evaluate each area more frequently.