Here is a software-independent great step-by-step guide. It's done by Wooden Palette, and their site has all the details to make it happen (this is more of a summary to explain the basic principles behind anamorphic art.
STEP 1:
Create a simple grid (or use an existing one).
http://www.woodenpalette.com/wp-content/uploads/2014/02/grid_1.jpg
(source: woodenpalette.com)
STEP 2:
Create a perspective plane. You can use a copy of your existing grid, and flatten it. The amount of flattening will depend on the position of the supposed person looking at the drawing.
http://www.woodenpalette.com/wp-content/uploads/2014/02/grid_2.jpgSTEP 3:
Place your art on top of the grids.
http://www.woodenpalette.com/wp-content/uploads/2014/02/grid_3.jpgSTEP 4:
Stretch both your art and the flattened grid back to full height.
http://www.woodenpalette.com/wp-content/uploads/2014/02/grid_4.jpgSTEP 5:
Stretch the art and former flattened grid to full width. Your second grid and your first one should overlap perfectly. Voila! Your anamorphic art is ready to be applied!
http://www.woodenpalette.com/wp-content/uploads/2014/02/grid_5.jpg