Cigarettes
First of all, cigarettes are not appropriate for branding unless you are looking for something that will look like, well, a cigarette burn — flat, round, and inconsistent. Hair will usually continue to grow from them. They can be tattooed over, but even then they may still be visible to some extent.
The real reason this entry is here, though, is to note the effects of cigarette smoking on the healing of body modification procedures.
In the case of oral procedures such as tongue piercing, lip piercing, tongue splitting, and so on, cigarettes are an easy way for bacteria to get into your mouth. If you have to smoke while healing a modification of this type, make sure you have clean hands, under no circumstances should you share your cigarette, and rinse afterwards. It should also be noted that the fresh smoke can kill tissue that it comes in contact with, both increasing your chances of infection and slowing the healing. So keep your smoking to a minimum (try and stop!), or switch to a patch if you can.
In more general terms, smoking both weakens your immune system and damages your circulation — both things which are essential to healing. Quitting smoking is not only a good idea in general, but it will help you heal your body modifications more easily — and this in turn will result in a better looking tattoo, piercing, or modification.