Now we'll start to separate the elements of the image further.

Select a slightly darker shade of Gray , and again using the Lasso Tool, start tracing large elements of your image. Once you've done this, color it with the shade of Gray you've chosen.

Select another shade or Gray (darker or lighter is your choice at this point), and again with your Lasso Tool, separate smaller elements of your image.

Keep doing this until you've separated every element of your lineart like the teeth, lips, eyes, iris, etc.

TIP: At this point, how you separate the elements of your image is at your disgretion, just make sure that you DO NOT use the same shade side by side.