One of the key elements to consider, when trying to draw an object to relative accuracy, is negative space, this space is the surrounding, in-between and isolated shapes that are not a part of the physical image. Mastering the negative space leaves you in a great position to get the positive space in correct proportion. This technique helps you to establish a background first before the foreground, which in turn helps you gain a sense of difference between them.
Another few techniques are tangents and axis’s. They are both used in similar ways but an axis is the line that travels directly between two shapes. This can help you gain a sense of balance and alignment to the piece. Tangents are lines we add to edges within the subject to aid proportion.
When finding order and proportion in my own sketches I found that using these techniques helped me to realise how difficult accurate drawing can be, and opened my eyes to how originally wrong I would have been drawing free hand. I feel if I pursue these techniques daily I will become skillful in my sketches in the future.