For each of the line drawings below, try doing versions of all 3 major strategies: Pos-on-neg, neg-on-pos and a dynamic pos/neg relationship.    After you finish you can compare your value studies to the finished versions posted there.  Remember that there are countless correct solutions to this, but the important thing is to keep your silhouette clear.  You can download the full-size drawings or post your finished versions for comment at: www.hyperspacestudios.com/reinventing/exercises