Clipping a ferrets nails is best performed by two people. One holds the ferret by the scruff of the neck in one hand, using the other hand to help support the ferrets weight, while the other person gently clips the nails. Don’t clip them too short, you can hurt the ferret.
Performing the clip job one handed isn’t nearly so easy. I find that putting some FerretVite or FerretTone on their belly distracts them long enough to get the job done. While they are licking their belly, you are clipping away!