I use human nail clippers. It is really easy, like cats, you can see the quick, and don't cut it, so only trim where the nail is clear, on dark nails a flashlight can help.
However, cut the nail like you would if it was your own. What I mean by this is don't put it in side ways or you may crush nail that should be left intact and hurt the quick. Place the nail into the trimmer with the bottom of the nail against the bottom of the trimmer, kind of like this:
and not this:
the straight lines being the nail clipper top and bottom, the triangle the nail itslelf.
Perhaps guinealynx has some better info??
EDIt: Added: If they are really long, and you are really afriad, just trim a bit, and the quik should move back, and in a few days, trim a bit more...
I noticed my piggie's nails need a trim, or at least I think they need trimmed. How long should they be? How do I trim them? I have a cat nail trimmer tool, will that work? I'm so afraid I will trim them to low or hurt her!
Thanks for the help!