Stixnstonez is a really easy tangle to shade, simply because there are so many options. Really, anything goes, but consistency is the key here. In this example, I created heavy pencil markings in the middle of each square and then used my finger to “push” the color to the edges. If you look carefully you might see some partial fingerprints!
In the example here, I’ve lightly shaded the outer edges of the squares (a reverse of the first example in some ways). There is no reason that you shouldn’t shade the tangle itself, too—perhaps the circles (the first step in the tangle creation)—or create gradients across the whole tangle.
Keep practicing Stixnstonez here, now adding shading options. Try as many variances as you can think of.
Downloadable worksheet available at http://www.createmixedmedia.com/zentangle-untangled-workbook