I prewash the fabric remove from the washer and starch heavy, but I use the liquid starch, much cheaper than the spray.
I use 4 to 5 cups of starch to 1 cup of water.
Soak for a few minutes, squish it all around making sure the fabric is soaked good, then squeeze it out and throw it in dryer.
When done starching the fabric I just pour it back into the container, mark the starch container diluted.
If you are going to do light and dark fabrics, do the light first. If you have lots of starch in your bowl after doing the light fabrics then put some it back in the bottle before putting your dark fabric in the starch just in case if fades a bit.
I got a oblong plastic container at Walmart.
Good luck and enjoy
Pam