As obvious as this seems, baby bottles must be kept well clean and sanitized for as long as they are used by baby. Bottles, rings, tops and nipples should be sterilized for every use for months after baby is born. In addition, while you are sterilizing bottles, throw the pacifier in as well. Make sure your hands are clean every time you handle babys bottle and supplies. Once your baby is older, constant sterilization is not as important, but sanitizing them is. Since it only makes sense to sterilize several items at once; pacifiers, nipples, rings and tops can easily be kept in a Ziploc bag that has never been used. Bottles can as well.
While your baby is still young, do not put a bottle from the floor back in babys mouth; it will not hurt your baby to cry while you fix another one. This goes for a pacifier as well if sterilization is not possible, or a sterilized one is not available, run it under very hot water for a few minutes, then cold water before giving to baby. Sterilizing can be done using a specially made unit for bottles, or over the stove in boiling water.
A newborns digestive tract is not yet developed fully and does not tolerate germs well. For this reason it is important to keep as many germs as possible out of babys mouth. Important hygiene for you and your baby, as well as babys environment, is important for babys good health. Babies need time to build up immunity to germs. So, regardless of what others may tell you, sterilization is important for the newborns feeding supplies.
Once babies begin crawling and moving around, its more difficult to keep everything he touches sterile; therefore, babys immunity system is better developed and sterilization before every use may no longer be necessary. However, cleaning them thoroughly in hot water is very important. Its not likely that you will ever make anything too clean for your baby.