Techniques
So when starting to draw, try not to have too definite a view of the end product. If the picture you are doing is imaginary, even if based on a real subject, you can include anything in it, including the improbable and impossible. Fantasy pictures are immense fun to do and may have some therapeutic benefit. If you know the rules, it is sometimes refreshing to forget them, and have different perspectives in the same picture, or even eliminate perspective altogether.
Composition
There are several terms common to all arts. Composition is the arrangement of the parts or elements of a work of art. These individual parts or objects are often called forms, but the word form is also used for the total character of a composition. The study of the composition of works of art is called formal analysis. Basically, this is taking apart a piece of art and studying its basic shapes.
Formal analysis is useful to the beginning artist because it shows you how other artist have approached the problems of catching a subject on paper or canvas.
Line and Space
One of the problems in most drawings is creating the illusion of depth. One method is to create perspective in a picture by using an imaginary point, called a vanishing point, somewhere in the background, usually on the horizon. The lines of the objects in the drawing converge on this point, depending on your subject.
Shape
There is much disagreement among artists over three terms: shape, form and mass. A shape is any area with clear boundaries. It can be graceful or clumsy, rigid or fluid. Shape has only two dimensions, length and width. Positioning shapes, such as overlapping them, can sometimes give the illusion of depth.
Form is a broader term. Form can include a shape, but will also include related shapes and shadows that create a coherent whole.
Mass requires depth, unless the subject is viewed on edge. Mass has thickness or roundness. Artists produce the effect of mass with highlights and shadows, and by the placement of shapes.
It may seem odd at first, but each shape you draw will define the space both inside and around it. Learning to see shapes in this way can help you draw and paint. To understand this, think of the shape itself as a positive shape, and the space around it as a negative shape. Every positive shape makes a negative shape. Examining your subject in terms of its shapes can help you overcome the two-dimensional barrier.
Value
Variations in lightness and darkness are called variations in value or tone. They are used to define shapes, to create mass, to emphasize special parts and to express feeling. Modeled light and shadow is used to reveal the shape and texture of an object and can give subtle or dramatic emphasis to various parts. Contrasts of light and dark shadows are often given the Italian name chiaroscuro.
Texture
Texture is the pattern of contrasting surfaces found in every object. A surface can be rough or smooth, hard or soft. In drawing we capture texture with various techniques of shading. Cross-hatching, hatching and stripling are only some of the techniques available. With a pencil, you can shade by using the side of your drawing tool. You can also use your fingers to smudge your lines, or an eraser to lighten and spread them. All these techniques will help give your subject texture, and therefore volume. In painting, texture also refers to the quality of the paint itself and how it is applied.
As you can see, these terms are interrelated. It is difficult to talk about one without mentioning the others.