Matching sets get bought for the co-ord look and then worn exactly that way until it feels done. The value is in the fact that you own two separates that already fit you well.
One: as intended
Worn together, a set does the deciding for you. It reads considered because the proportions were designed against each other — the crop of the top against the rise of the bottom. Keep the rest minimal: one bag, one pair of shoes, nothing competing. This is the version that photographs well and takes ten seconds to put on.
Two: split the top
The top half of a set is usually the more versatile piece. A ribbed or striped tank sits under a jacket, over a longer skirt, or with jeans, and none of those read as sportswear. Because it was cut to sit at a specific point on the waist, it tends to work better tucked than most standalone tops.
Three: split the bottom, add contrast
Shorts or a skirt from a set paired with something oversized on top is the easiest way to make a co-ord look unplanned. An oversized hoodie or a loose overshirt against a fitted bottom half gives you the proportion contrast that the matching version deliberately avoids.
A note on print
Heavily printed sets are harder to split than solid or striped ones — the print reads as belonging to its other half. If you want a set that gives you three outfits rather than one, buy the plainer one.
Care
Wash the two pieces together, always. Colours shift slightly with each wash, and washing them separately is how a set stops matching.