The Shulchan Aruch Orach Chayim 260:1 says that it is a Mitzvah to trim one’s nails on Erev Shabbat i.e. Friday. The Rema adds that if one’s hair needs a trim, then one should do it then as well. He also adds that we do not cut the fingernails in order. We should begin with the left hand starting with the fourth finger then move to the second then the fifth, the third and then the thumb.