Draw your imagination. Draw what's in your head
This is a sentence which is a little bit overused at this point. The most important what you need to realize is that first, you will need the proper knowledge and a good deal of exercising for you to be able to draw what’s exactly in your head. Even the biggest artists fail sometimes and they simply cannot mirror what’s in their head. That’s why so many of them use models, no matter if it’s about a subject or a person, because even they do need to actually see how the shadows and the lights fall onto that specific object from a specific angle.
It would be great if we could simply put everything on paper and it will eventually happen, but up until then be patient, learn how to draw properly and keep on exercising, by drawing everything you can actually see.