Start a necklace stack with one piece you already wear often. Add a second chain at a clearly different length so each necklace has room to show. If the lengths are close, the pendants may land together and the chains can twist around one another. A shorter plain chain paired with a longer pendant necklace is a simple, flexible combination.
Varying chain styles can add definition, but too many competing details may make a stack feel busy. Try one delicate link beside a slightly bolder chain, or mix a pendant with a plain strand. Keep the overall scale in mind: a large pendant can be the focal point, while smaller pieces support it. There is no need to use every necklace at once.
To reduce tangling, put on the shortest necklace first and fasten each clasp before adding the next. Some people find that a layering clasp helps keep chains separate, though it is not essential. When taking the stack off, unclasp the pieces instead of pulling them over your head. Store necklaces flat or individually so they are ready to wear again.