I have made a rubbing of my mountboard plate by lying layout paper (which is very thin) over the top of the plate and using a graphite pencil to get an impression.
I scan or photograph the rubbed image onto my PC and open it in Photoshop. Since the lights and darks of rubbing itself are the opposite of what my final print will look like I invert the black and the white in Photoshop to see what it looks like.
This gives me a very good idea of where the lights and darks will be when I do my final Collagraph print.
See now how the wing is now the highlight and the underside, eye area and lower beak is dark.
On the plate itself these highlights also have wood glue (or you can use PVA) which help to create brighter highlights on the finished print.
I am happy with this; now for the inking and printing!