I highly recommend Mr. Hillberry's book. He is the best at drawing different textures and demonstrates exceptionally well how to handle metal surfaces!I always study the particular item for 10-15 minutes and try to see as much detail as I can. I lightly sketch the outline of the item and most obvious areas, then I start drawing the details, the shadows, the seams, etc. It works best if you draw the details that you see instead of drawing the item as a whole.
I know when I start drawing familiar items I usually end up drawing what I think they look like instead of what I am looking at.
Sorry if that's confusing....I am not very gifted at explanations!
Thank you
D.L. Hesse
www.artinpencil.com