I always start with a compression test along with inspecting or just changing all the plugs while they are out. Also inspect all of the ignition coils. If compression was good I swap coils from the misfiring cylinder to a different one and see if the misfire moves with it. Also, while the engine is running use a long screwdriver or something similar, put one end on the body of the injectors and put the other end to your ear. Should be easy to hear the injector firing, you will hear a lot of clicking.