When I'm working on an illustration, I try to include handmade and organic elements so that the illustration doesn't feel entirely created in the computer. I think it gives it a more unique, more imperfect feeling. That could mean drawing or painting and then scanning it in to use, or perhaps scanning fabrics, paper or other found objects. This example is an illustration I did that needed some texture to it so I took the left over coffee grounds and dropped them around on a piece of paper, then left it out in the sun to dry. The next step was to scan it in and adjust the contrast, then take that file into Adobe Illustrator which is my absolute favorite program for drawing. In Illustrator the texture was then colorized and layered into the background of the snail party which gives it more depth and interest.
The top image is the texture I made and the bottom image is the finished illustration.