You need: a lightbox, a reference image (the thing you want to trace), and a blank sheet of paper. Oh, and tape. Scotch tape, masking tape, or that weird duct tape your dad uses for everything—it doesn’t matter.
You also need good lighting. If your room is darker than a movie theater during a sad French film, you’ll strain your eyes so hard you’ll see sounds. Seriously, tracing in the dark is how you end up with a drawing of a raccoon that looks like a melted potato.