Note the similar target area in (D), but with a significantly smaller brush. The result this time (E) is much more in keeping with expectations.

So—
Rule 1: always keep the size of your brush in proportion to the artifacts that are being dealt with. Even if the overall area that you cover with a single move is much larger, the tendency to pull in unwanted pixels will be determined by the brush size. (On the other hand, if there is a sharp transition that you want to smooth out, replicating the "mistake" of image (A) can become a valued procedure. A few passes on either side of the transition line, pulling the regions into each other, can make for smooth transitions.)

Rule 2: Don't use the healing brush to make drastic shifts in color or value (i.e. removing a dark shadow, or a necklace.) It will make a soupy mess of the job. Prep the area first by using the Dodge/burn techniques or the color moves discussed next, to bring the target into rough balance with the surrounding area. You could even use the clone tool.

Note the similar target area in (D), but with a significantly smaller brush. The result this time (E) is much more in keeping with expectations.

So—
Rule 1: always keep the size of your brush in proportion to the artifacts that are being dealt with. Even if the overall area that you cover with a single move is much larger, the tendency to pull in unwanted pixels will be determined by the brush size. (On the other hand, if there is a sharp transition that you want to smooth out, replicating the "mistake" of image (A) can become a valued procedure. A few passes on either side of the transition line, pulling the regions into each other, can make for smooth transitions.)

Rule 2: Don't use the healing brush to make drastic shifts in color or value (i.e. removing a dark shadow, or a necklace.) It will make a soupy mess of the job. Prep the area first by using the Dodge/burn techniques or the color moves discussed next, to bring the target into rough balance with the surrounding area. You could even use the clone tool.