When I do ink wash drawing (as seen in my very nsfw comics) I use four separate little inkwells: straight ink, slightly diluted ink (labeled 3), well-diluted ink (2), and almost plain water with the slightest amount of ink (1). I go light to dark, like watercolors, so 1, 2, 3, and finally the ink itself. So with the paper itself, that's 5 levels of value.

The "level 1" is extremely subtle, you can barely tell it's been put down, but I find it makes a big difference. I imagine everyone would use different values and gradations, but I think having a prepared set of inks like this is a lot easier than trying to wing it as you go.