When the lower layers of your skin are damaged, scars can occur as part of the natural healing process because the body can not completely match the shape and texture of the damaged tissue.

The best way to avoid scars is to avoid any damage to the deeper layers of the skin. This is of course not always possible when engaging into S&M but simple changes like replacing a thin crop with a ticker one or a softer whip can already prevent scars.
Once you have sustained damage to the skin that can cause scaring there are still many things you can do to avoid the development of visible scars. First and foremost, it is important to keep the injury clean and free from infection. Dirt can become enclosed in the new growing skin and cause problems later. Infection will cause the healing process to slow down (or even reverse). This causes the scars to become more discolored and often virtually texture free.
Aside from antibiotics, there are few proven methods to reduce scaring. Dietary Vitamin E supplements help some while others react allergic to the high amount of the vitamin. Also, if the location of the injury allows for it, butterfly band aids can become very handy. They pull together the skin, reducing the area the scar tissue has to cover.

Once scars have healed, there is no way to completely get rid of themcompletely. Most over the counter treatments limit themselves to covering up the scar tissue or changing the color of the scar to make it less noticable. Only health care professionals have access to other methods like laser treatment, steroid injections and surgery that reduce the actual size of the scar.

The enhancement of scars as body art goes back several thousand years. All methods center around either making wider injuries in the skin or purposefully introduce substances that will be embedded in the skin during healing.
Scars made by branding or carving are usually wide enough for the development for large scars. Smaller cuts can be cut further with a scalpel or they can be bruned to create larger damaged areas. Tattoo ink can be rubbed into the skin. Other inert materials like ash or clay can be packed into the cuts as well. That creates stronger pain than ink and usually results in slower healing but the resuting scars will be raised and will be fairly hard to the touch.