There is no one cut and dried method or software it would depend on how the artwork comes to you, a lot of folks use a tablet to draw/trace directly into photoshop/illustrator/corel, although if presented with a drawing scanning the art is also another way of digitizing it.
The other thing is you have to keep in mind which printing process is going to be used, some processes require vector art (illustrator/corel) and some can use raster art (photoshop) but you can figure the bulk of the people here are designing in photoshop and if they need it to be a vector their importing it into illustrator or corel and converting it, or just creating it in illustrator or corel.
Hope this helps.