and prepare a paper, a pencil, and an eraser
First, imagine something unique. I just imagine a water-drop.
from it I'll draw a concept of an Aircraft. (draw it in from half-behind angel, so the 3D shape will be appeared, and dont forget draw it with thinly line )
next, add other stuffs, like shields, rockets, lamps, or what.
(draw it in where do you want).
when you draw, and find something not fix with your desire, you can clean up and redraw again
After it, try to fix it with your imagination and your draw. then, you can add it your original details.
if you want to draw from others side, approximately you can do it like before, beginning from making the simplest form of it.
and if needed, add description on your concept.
try to do it. :D