These are my absolute favorite shoes! They turned out a lot better than I hoped, too. The time it takes is probably off; this took somewhere between 5 and 10 hours. (But that's probably just because I work slow)
More detailed pictures of this pair can be found here: http://misfit-mistress.deviantart.com/gallery/30981227
First, aquire a pair of canvas shoes. They don't have to be anything pricey. I got mine at payless.
Next, sketch the design you want to do on the shoes with pencil. If you draw lightly enough, you can erase parts.
(Optional) If you are worried about getting paint on parts of shoe you don't want to, take over those parts with painter's tape or masking tape.
Start painting with a base coat for the background of your design. I chose yellow :)
Continue painting the design one color at a time, until it's competely filled in.
If desired (and it probably will be) outline your design using a thin sharpie or other thin permenant marker.
Finish off by coating the shoes with some sort of spray fixative, preferably a matte finish. Look for one that is UV and water-resistant and good for use on outdoor work. I bought mine (not the brand pictured) at JoAnn's.
Once the fixative dries, you're done! Now go out and show off your awesome shoes!