The elements of drawing
Let's get a bit more in depth with the elements of drawing...Line
Line is the most basic element of the drawing. And in it's most basic definition, it's what separates one area of the drawing plane from the other. A single line will segment your piece of paper into "that area" and "this area". The more lines that are added, the more complex and numerous the separations become: light from dark, foreground from background, positive space from negative space. Line can be uniform and all one width, or to be more interesting, and to convey more information with a single line, a single line can be of varying widths.Shape.
Shape occurs when the first line is drawn. The most basic definition of shape is the white area on the paper. Shape is the information that is presented between two or more lines, or is the thing that is enclosed by line. Shape helps define the object that is depicted as much as the collection of lines that make up the object in the drawing. Incorrect use of shape will cause the drawing to "not look like what it's supposed to be."
Click to see examples of each element of drawing.
Proportion and Perspective. Proportion is the size of one picture element in relation to the size of another. In other words Proportion is what dictates that, in humans, legs are longer than arms, the middle finger is longer than the pointer finger, and the nose is the same length as the width of the eye. If proportion is incorrect in a drawing it "doesn't look right". Perspective is the illusion that further away things appear smaller. To make something appear to be farther away from the viewer than the picture plane, draw it smaller than the object that is closer to the picture plane. I've put proportion and perspective together as one drawing element because they both use each other to work. If one is incorrect, chances are the other is also incorrect.Light and shadow.
Light and Shadow create depth and atmosphere in a drawing. In order to make a drawing look "realistic" you need shadow because in the real world everything has a shadow. If you draw something with only one width line and don't render shadow, your drawing is going to look flat, two dimensional, and unrealistic. Adding shadow automatically adds a small bit of perspective to the drawing because the shadow indicates that something is in front of and/or behind the object that would cause it to cast a shadow. The whole drawing
The whole drawing. Before you even start the drawing you will begin to automatically mentally place your picture elements on the paper. You take into account the whole drawing surface and relate your picture elements to the shape of your drawing surface. For example, if you're wanting to draw a whole human body from head to foot you would mentally place the head to one side (or top or bottom) of the drawing surface so that would give you enough room to be able to draw the whole body and not run off the paper. The shape of your drawing plane will help determine the composition of your drawing. You would not effectively be able to draw a towering skyscraper on a square piece of paper without cutting the top or bottom off. In the example on the right, seeing the whole drawing means when you start, you know where to place the eyes so the face will be in the center. Also, knowing that the tie will run off the page is being aware of the whole drawing.
Source : http://www.learn-to-draw.com/drawing-basics/05-drawing-elements.htm