How To Line Up Documents For Printing Front And Back In Illustrator?

I am printing a set of cards, and they have a design on the front and back. I need to know how to set it up ao that I do not go over the edge on either side. I am using adobe illustrator, but I can print them in jpeg or pdf format if needs be, they are not so big that they would lose quality, but obviously I would rather keep the illustrator files!