It's important to plan our values before we go ahead and render an image. Without good planning we're in danger of getting off on the wrong foot and most certainly will end up with a muddy looking image. Values should be organised into a narrow range that suggests the overall mood. This is basically how light or dark your image is, overall. A low-key value range will mean our lightest values reach only as far as half way up the scale, and a high-key value range will mean our darkest values reach only half way down the scale.
In both low and high-key images we can add the missing values sparingly to play with the drama. Dark clouds with silver linings, for example.
Next time you produce a sketch, spend some time experimenting with key before you dive into the rendering. Make as many variations as possible until you identify the correct key for your story or mood.
There's a lot more to talk about with value so we'll explore this in upcoming tutorials and tips.