Removing the dark stains that can get onto your hands from working with walnut and other dark woods can be easy. Just pour a little lemon juice in your palm and rub your hands together. The slightly acidic lemon juice will remove the stains from your hands without damaging your skin.
If your wood gluing work is less than successful, check your blades. If the blade in your saw is getting dull, it can loosen (but not remove) a layer of fibers on the edges to be joined. Later, glue may not be able to penetrate through this debris to solid wood, resulting in weak joints. A signal that this may be the problem is if ruptured joints are coated with fibers.