In my forum on Etsy "Do you need Help with anything Photo -Digital Related?", I mention fill cards a lot .
They are very easy to use and everyone has them around.
really low end... a couple pieces of cardboard -one painted black and the other with a piece of white paper taped to it.
The first one is called a *Positive fill* (This is a White card folded in half ).
This just bounces light into the shadow areas of your subject and adds a highlight into anything shiny. This is perfect thing to use when shooting on a black background because the black surface sucks up all the light.
I shot the above ducky in shadow light. There was barely any light coming in on the fill card when I was shooting. The more light on the card, the more fill...simple, huh?
The next is *Negative fill* ( This is a Black card folded in Half)
This is perfect when shooting on White, because the white surface bounces SO much light around, it can wash out your subject and take all the shape away.
Sometimes you might need both cards... or you might want to wrap a little tin foil around one to add a bit of PUNCH!
I suggest getting all of them together and messing around with them to see what each one will do for you.
Also, look at them on your computer to see the results, because it is hard to make any decisions while looking at he little screen on the back of your camera.