Piercings on the penis head, penis shaft, or on the scrotum are really no different than an ear lobe piercing, or a piercing anywhere else. They are all unnatural holes in your body, and your body treats them all the same way. A genital piercing is in no more danger of infection than any other piercing, *if* you follow the rules your piercer should have told you.
1. No sex for as long as you can stand it or 6 weeks. Sex prolongs the healing process if done before the 6 week mark.
2. No unprotected sex of any kind for 6 weeks, period.
3. Never touch your piercing without washing your hands first. The same goes for other peoples hands. Hands are the #1 transmission agent of germs around the body, to and from the enviroment around you.
4. Soak your piercing with "hot as you can stand it" salt water twice a day.
5. Use a very mild, unscented soap, to wash your piercing when needed.
Sex is your biggest enemy. Physically beating on the piercing is obviously not good while healing. What your penis might collect in the piercing while having sex is the killer tho. You don't want that, thus the protection. An infected penis is garaunteed to ruin your day. You skin is the best defense against infection your body has to offer, and you have an open hole in it.
Second enemy is the warm and frequently moist environment that your penis lives in. A change of clothes, underwear, or even freeballing may be a necessity to change to a cooler, dryer, environment that isnt an ideal bacterial breeding ground.
Stay away from hydrogen peroxide, alcohol, cleansers, bactine, ointments, all of that shit. This stuff either hinders, or stops, the new cell growth you need to heal, or will trap bacteria and lymph in the piercing, leading to infection. Salt water, super mild soap, and even the LITHA method is the recommendation of the good pro piercers.