1: A jacket made of something sturdy but not too thick. You will be putting a lot of pins into this thing, so thin fabric is likely to tear. Fabric that is too thick will be harder to work with. (I've used a few denim jackets before, which have worked pretty well, but something like polyester or a wool blend is easier.) Jackets with lining are nice, because then it is possible to hide the backs of the pins by only pinning through the top layer of fabric. Also, choose something with a simple pattern that won't overwhelm your pin design.
2: Safety pins of various sizes. (For this jackets I used size 0, 1, 2, and 3 steel and brass pins.)
3: A light colored pencil or chalk
4: A needle and thread
5: Optional: a dressmaker's dummy. This is very useful because it lets you see the overall effect of the image as you work. I like being able to constantly see what the worn jacket looks like, but working this way is harder on your arms. You also need to be careful not to pin th jacket to the dummy, as many of them are fabric-covered.