What do you consider before starting a drawing? An obvious choice would be to start with your subject. Then, maybe you consider the composition and how you want to place your subject. What you want to include verses what you might choose to leave out. Which medium you intend to use, etc. How much thought do you put into choosing a background tone? If you aren't thinking about these options, you are missing an opportunity.
A tone is the relative lightness or darkness of a color.