There are three ways of realistically representing an object with drawing. One is by using line to describe the form of an object. Another is by using tone (darkness and lightness including shadows and highlights). A third way is found in the union of these first two, using line and tone in the same drawing.

Perception

Humans have binocular vision, which means that we see in 3 dimensions. One of the problems in learning to draw is translating these 3 dimensions (Height, width, and depth) into the 2 dimensions of height and width on your paper.

One way to solve this problem is to copy from photographs because the image has already been flattened for you. This will not help you learn to draw from reality though.

Another way to help solve the problem is to close one eye at times when drawing. This causes your binocular vision to become "uniocular" and serves to flatten your perception of depth.

Drawing, like all art, is about expressing the essence of something. It is difficult to achieve this when first starting out but with practice you begin to forget your tools and concentrate on what you want to say with your tools. Just as when you first began to drive a car you concentrated on the pedals and the gear stick and the stearing wheel, and your quality of driving wasn't that great, when you continued driving these things simply became automatic and you could drive better without thinking about how to change down to third. So if you keep your mind on what you want to show rather than how you are doing it then, with practice, your hands and tools will follow.

Drawing will give you an insight into the structure of things and ultimately an understanding of the purpose of that structure. Leonardo da Vinci was one of the first artists to understand that nature's unique structure is a result of it's unique function - it would not look that way if it didn't have a purpose in looking that way. An example could be a tree branch which joins the trunk with a certain thickness at a certain angle. It looks like that because that is the best possible structure for its purpose, which is to hold up the rest of the branch through all seasons and weather.

So when you are drawing something you are learning about it. From that point on you will have a greater appreciation of that subject; that flower, that bird, that mountain, and you will begin to look at all things in a more inquiring, appreciative way.

Step by step

1. Determine the size and placement of the object on your page.
2. Lightly rough in the basic shapes in proportion to one another.
3. Start refining the smaller shapes, still sketching lightly.
4. When you are happy with this medium level of detail begin darkening the lines - not slavishly copying over what is there, but comparing what you have drawn with the object and making adjustments as you go.

Pointers
Close one eye to flatten the image.
Compare CONSTANTLY - as soon as you stop comparing your accuracy will be lost.
Sight angles and sizes with your pencil.
Varying the thickness of line will add more character and vitality to your drawing.

Advanced pointers
The part of the object which is closer to you can be drawn with stronger lines to give a better sense of 3 dimensional depth.
Part of an object which turns away from your vision sharply can be represented by a lighter line than can that part which turns away from your vision less sharply. eg. the line of an arm is thickest where the arm is roundest at the bicep and thinner at the elbow where the bone makes a tighter corner (making the arm disappear from view more sharply)

Project #2
Select an object which has a more intricate structure than the last and draw this in the same manner.

Notes:
If you begin by drawing detail first you will always get the drawing wrong.
"Work Big to Small and you can draw"
When you can draw REAL things it becomes much easier to draw things from your imagination.