You should try to keep the one viewpoint in mind, to be careful of the perspective, to draw additional helping lines (the grid, the axis, the central line, etc.), and always measure one part of the object in relation to another (measure height according to length for example, or distance of one object in relation to other distance)
Explanation:
The proportions are the basics of realistic drawings and they include the lifelike relations of the objects, the same observant spot, and the correct positioning of the objects, and the good measurements.
First, you must make sure all objects on the drawing are presented as seen from the same angle and point of view. That means you should have the one perspective point, and draw all things shown as seen from that point.
The second is to have a good perspective on things. The lines should not be completely straight, but they should go closer as the object is presented as “further”. These imaginary lines at the edge of the object should meet at one vanishing point on the horizon. This means your perspective is good.
It is a good idea to draw a grid on the paper first in thin lines. This way, you can separate parts of your drawing, and see how they relate to one another. The grid is especially useful when drawing something from the photography, as you can draw the grid on the photo as well and copy one part after another. It is always useful to lightly position the central line of the object, to see where the middle is, and to the position in accordance with it. This also can help you maintain the balance of the object.
You should always measure the elements of the object you are drawing. This means you use a stick or a pencil to measure one part in relation to another – is it bigger, smaller, how many times is one included in another, etc. They should always be measured relating to others to show genuine proportional. This way, the object will have correct realistic measurements, and no part will be shown as different in relation to others. If you put the central line on the object, you can also measure in accordance with it. Be sure to also portion the correct distance from one object to another in the same way.
