So this is how I usually start a t-shirt design.  A small sketch in my sketchbook.  It's usually done pretty quick just to get the idea down.

Because I wanted to make this design look like a vintage horror poster I did some research and then did this mock up sketch full size.  However, since the final illustration would be graphite I needed to use this version as a background and draw a cleaner version using this one as a guide on a light table.

Here is the final illustration done in graphite - no Photoshop.

Close-up of final.

I took a slew of macro pictures of erasers to use for the design.  I used the paperclip to hold it in position so that I could easily Photoshop it out without casting a shadow.

Final illustration.  The eraser dust I just threw on my scanner and added in last.

Mock up of it on a tee.

Printed product picture at Threadless.