Some further work on my Illustrator skills following along with Toby Leigh’s tutorial at http://www.digitalartsonline.co.uk/tutorials/adobe-illustrator/create-retro-style-comic/.
I started by doodling a funny boy using cheap markers. Then I scanned it in 300 dpi and vectorized it in Illustrator. For colouring I used photoshop with halftone filters (Filter -> Filter Gallery … -> Sketch -> Halftone Pattern). To enhance the retro effect I downloaded an old paper image from the Internet and used it on top of the color layer with the overlay blending mode.