I agree with the timing thing, dd fights like crazy if she is tired, so I always do it just after she has woken up.
I sit her on my lap, but I file her nails instead of cutting (using a cardboard emery board, not a metal file), I give her another nail file to hold, which seems to distract her...she has even started copying me & trying to file her own nails.
Also I sing a song about different fingers to her while I'm doing it.......
e.g.
Tommy thumb, tommy thumb where are you.....here I am , here I am how do you do?
Then the same for all the other fingers with their appropriate descriptions & names.
Sometimes I might only get one hand done a ta a time before she gets fidgitey, but I just do the other hand after her next nap.
Good Luck