Newborn babies have such thin, sharp fingernails. Many come straight out of the womb in the need of a trim. It's very important to keep a baby's fingernails trimmed because they are so sharp. Many babies scratch their faces up something horrible with the tiny nails. Not only that, but because babies put their fingers in there mouths so much, it's just more hygienic to keep them shorter.
Special, made for babies nail kits are available at nearly any place that carries nursery items. Many people often even receive at least one set as a shower gift. The clippers in these kits are smaller, and more suitable for trimming the nails of a small baby. Try trimming the baby's nails when he/she is sleeping. This might be the only time the baby is still enough to be accurate. Make a small clipping at one side, then progress across the nail in a straight motion. Be very careful not to clip into the nail bed. If you happen to clip the nail bed, treat it with a cotton ball and a small amount of rubbing alcohol, so infection does not occur.
For those who are worried about clipping into the nail bed, or those who have unsteady hands, try filing the names down with a soft emery board. These usually come in the nail kits for babies. This will rule out the possibility of clipping to far. Blunt ended nail scissors can also be used, but some people find these more difficult to use than others. Finding something that works best for you and your little one is the most important objective.
If nothing else, many people bite their infants fingernails off. This is not such an issue if indeed the mother is the one doing the biting because they usually share the same germs. Assuming she is well. However, please do not let someone who does not live with you do this. I remember when my son was an infant, a distant cousin of mine ask to hold him. She then proceeded to bite his nails down. I was so repulsed, yet speechless.
Babies nails might require frequent trimmings as often as twice a week. Use baby emery broads to gently smooth out the rough edges. In between trimmings there are mittens that can be used over their tiny hands. These prevent babies from scratching theirs faces. Once babies get old enough to take baths, use a soft brush to gently scrub the nails.