Found a dirty sheet of paper that I've used as bleed through paper. Didn't want to waste it so put down a quick doodle on it while sipping on my second cup of coffee with @ericprydz - Opus blasting through my headphones.
The build up in that song is at the same insane level as @deadmau5 - Strobe.
Yeah, I said it.
Great way to start the weekend.
Anyway, if you only have a pen to sketch with, line weight becomes more important. You can add a sense of depth by adjusting the thickness of your lines.
To do this, you need to know where your light source is. Where is the light pointing? In this case, the light is coming from the top.
This means that the edges that are facing away from the light source will be thicker.
It's easy to get a hang of as long as you keep your direction of light consistent.
Try it! :)
//Marouane