It is preferable to clip the fingernails in the following manner:

Start with the index finger of the right hand and clip towards the little finger. Thereafter, start with the little finger of the left hand and clip towards the thumb. And finally, clip the thumbnail of the right hand.

A person should start clipping his toenails from the small right toe and end at the small left toe. (Hindiyyah 5\358)

This is not a sunnah however, it is preferable. (Ahsanul Fatawa 9\82)