The difference between "styled" and "cluttered" layering comes down to two things: length and weight. Get those right and almost any combination of chains works.
Vary the length, always
Two chains at the same length just look doubled, not layered. A short chain sitting at the collarbone, paired with a longer one that drops a few inches lower, is the simplest way to make layering read as deliberate rather than accidental.
Mix a thin chain with a statement one
Pairing a fine cable chain with a slightly bolder curb or paperclip chain creates contrast without competing. Two thin chains together tend to tangle and disappear into each other; two thick chains together can look heavy. One of each does most of the work.
Let one piece carry a pendant, not all of them
If every chain in the stack has its own pendant, the eye doesn't know where to land. Pick one chain to carry a pendant or charm and let the others run plain — it gives the whole stack a clear focal point.
Three chains is usually the ceiling
Two is easy. Three works if the lengths and weights are genuinely varied. Beyond three, layering starts working against itself — the individual pieces stop being visible as separate chains and start reading as one cluttered mass. If you're building a stack, that's the practical limit to keep in mind.