When my four kids were newborns and toddlers, I would usually clip their nails after they had a bath. The warm water made the nails soft and easier to clip. They also make baby clippers which are much smaller than the ones adults use. Good luck!
Although I clipped my sons nails with baby nail clippers when he was a couple of weeks old, I was told recently by a hospital nursery nurse that baby's nails should not be cut with clippers in the first months because they are soft and you run the risk of pulling that nail from the bed. She recommended scissors. Now that makes me a nervous wreck to even think of coming toward a newborn with a small pair of sharp scissors, but she has been doing this for 25 years. I would just be very careful with whichever method you choose and make sure that the baby is calm, sleeping preferrably. An emery board also seems like a viable option.
I never used clippers or scissors to clip my daughters nails. I tried using a nail file, but she was too squirmy for that. So I started bitting them. I would just bite the side to make a little cut then rip it off. This works really great for me. I still do it with my dd who is 14 months old.