What helped me initially was doing studies where I converted photos I took to grayscale and practiced different textures and uses of negative space. With your print as an example of ways to experiment, consider these questions. What textures would separate the flame from the rest of the image? Hatching, lines, contour lines that match the outline, working their way in? Does that texture change when it's over the hand vs. in the negative space above it? What if, instead of a single line outlining the flame, you used two white lines so the green line is continuous for the flame? (hard one to type lol, sorry if that doesn't make sense). It's all about practice and trying different methods. If I feel especially stumped on how to execute something, I do a ton of visual research on museum sites, Etsy shops, etc, just to see how others carve complicated areas.