Try to divide the object you want to draw into basic shapes.

Basic shapes are for example a circle, a triangle and a rectangle. The shapes may also differ slightly. (see image basic shapes)

First draw those basic shapes with a pencil. Then you add details and small deviations from the basic shapes. You can now trace the correct lines with a pen. Erase pencil lines, and the drawing is done.

The basic shapes will help you understand what you are drawing and gain control over the lines you want to draw.

Later on it becomes easier to apply light and shadow, when you used basic shapes in your set up. In Daphne's videos about drawing, you can clearly see how you can draw, using basic shapes.