Making large, bold shapes is more important than ever when working with darker skin tones. Because we have such a limited range to work with in our transitions, we need to make sure our shapes are very clear and visible to help boost their structure.
Unintentionally, we can make the piece more flat if we're not careful with our value decisions. We can avoid flattening out over time by defining our lights and darks clearly first, subtly adding transitions as needed will prevent the work from flattening out over the life of the tattoo.
Another thing you should consider is limiting the amount of planes you’re working with. This doesn’t just apply to darker skin, but simplifying to just foreground and background can make readability better on ALL skin tones.