I'd suggest running a Google search on mythology and foxes. Different cultures have different views on them. You will find them in both Japanese mythology as well as Native American only to name a couple.
Pay attention to what is stated about their characteristics if this is a spirit animal, you may be able to utilize some of these traits.
I also suggest running a search if you haven't already on Fox spirit animal.
Within the mythology of foxes you can pick a number of ideas to use within your practice. Many of these myths are based themselves on previous practices already. Use your discerning ability and sift through the information.
By the time you're done researching all you can about foxes within cultures, myths, and history, you will be well on your way to determining exactly how you wish to form and practice this as a way of magic.