On an inside pocket, if the hole or worn area is near the outside (free) edge, make a seam just inside the tear. To mend the pocket by hand, make two rows of backstitches. If you are stitching the pocket by machine, make one row of straight stitches; then put a row of zigzag stitches next to it in the seam allowance. Trim close to the stitches.
If the hole or worn area is within the body of the pocket, either darn or patch it.
If large portion of the pocket needs mending, replace it with a sew-on or iron-on replacement pocket. They’re available at notion or sewing stores.
Patch pockets often come loose at the upper corners. Tack the corners with straight machine stitches, and backstitch 1/2 inch. Or use narrow, closely spaced zigzag stitches. To sew the corner by hand, whipstitch for about 1/4 inch on each side of it.