There are any number of ways to disguise a mend or cover a stain. You will have to consider each case individually, using your own imagination and sense of style.

Cover-Ups

Depending on the location of the stain or mend, you might be able to cover it with a pocket, trim, or an appliqué.

The location has to be just right for a pocket to work. Even if it does work, there's the problem of fabric. Generally it is better to use contrasting fabric than it is to try to make the pocket from a near-match fabric. Use the fabric again around the collar, or match it to a new set of buttons. If it's a short-sleeved dress or shirt, you might stitch a narrow fold of your pocket fabric behind the sleeve band and extend it just ¼″ beyond.

Whether a row of ruffle or other trim is going to work will also depend on the location. Perhaps a second row in a more logical place will keep the first from looking odd. Maybe three rows of narrow ribbon sewn on the diagonal across one side of a casual shirt and repeated along the bottom of the other side will work, if the ribbons pick up colors in the shirt.

Children's clothes lend themselves to the use of appliqué for cover-ups. If the exact location seems wrong for a single appliqué, consider how it might look if it is part of a scattering of related appliqués.

Cut It Away

Consider how you might modify a garment to get rid of a stain or serious tear. If it's on a sleeve, can the sleeves be cut off above the problem and either banded or hemmed? If it's near the bottom, can the garment be shortened?

If the problem is in the center front of a sweatshirt or sweater, consider slitting the garment down the center, adding ribbing to cover the cut ends, and turning it into a cardigan.

Sometimes a neckline can be changed to remove the problem. You can use a near-match fabric to face your new neckline. Press it so the stitching is just under, rather than right on, the edge. This is a trick you might use to make something you're tired of look like something new.