If you find that you're having a hard time trimming your cat's claws - if they're upset and wiggling all over the place, or maybe just trying to kick you to death with their back feet, using a towel or blanket is helpful and will keep the cat from injuring themselves or you.
Wrap it around the cat firmly, leaving only their head and the paw you're trimming sticking out of the towel.
This will help keep them from fighting too much.
Make sure to reward your cat afterwards if you do it this way - chances are it stresses them out much more than you think! Give them catnip, treats or wet food and lots of pettings to help calm them down after.