I sit down on the floor with my cat, put their hind end on my lap, with their legs pointing out,(so they are basically sitting on my lap) I firmly "hug" them with one arm while pressing on the pad to get the nail out. Then I cut them. I use a nail trimmer that I got from Petsmart, specifically made for cats. I have been doing this since they were kittens though, and while they don't like it, they tolerate it. I've never cut to deep either, so they trust me enough to let me do it. Better off leaving them a bit to long than to cut to much off! I also talk calmly to them while I am doing it.
Another option would be to bring them to the vet or groomer and ask them to do it, or to teach you some tricks to use. I had a vet that would do it for about $12 for both cats when we lived out in D.C.