One thing I do is just use one type of brush and I find the chalk types to be good for this set at just one size, 50% opacity or so and pen pressure on, and one color (I go with black since my thing has been greyscales lately.) My line work is my line work and I just generally like working that way, but I try to build up my forms this way with as large a brush setting as I can manage and it helps me to problem solve tough spots. My stuff isn't pretty like a concept artist's, I'm no where near that level, but it does help me be more accurate in the long run I think at least
The important thing is to remember in digital work you really are NEVER limited by your 'mistakes' so why not just go nuts?! Most often it's more a mental technique than a straight up 'this is how you do it with these tools' thing.
BTW, for what it's worth, I thought you incorporated a very nice loose quality mixed with just enough focused detail in the right areas on your piece for Cancer