I know this is an overly cliched saying, but practice. This particular drawing you see is only my third proper drawing complete with shading, if you look at my gallery you'll see my previous pencil drawings. They were NO WHERE close to this and honestly, back then I didn't think I could pull this off. Keep practising and a get a good set of pencils. Helped me ALOT.
use tortillon boy! tortillon! it will blend your shading to give it a smoother look.
i think this is the best overall because of the sharp lines, notwithstanding it being an enzo.
not sure about the form tho.the farther door looks abit odd, like its not aligned properly. it's almost there i believe, but boy i know doing perspectives with symmetrical objects are a pain in the butt. kudos for the completion of so many drawings. u've been productive eh??