I have found that the best way to cut nails is to let someone else do it. Dino had it done sometime ago and they got the quick so now he pulls his paw back but does not show teeth or even growl.
I bought a pedi paws which is a low power battery operated Dremel style tool. I have heard that with bigger dogs there is not enough power in these tools, but I am in no hurry and would rather work a little harder than to quick a dog. Poop usually falls asleep upside down in my arms while I am doing his nails.
I use a manual cutter, backwards, so the blade cuts front-to-back, opposite the way the blade guard is designed for. Front-to-back seems more with-the-grain. Have an assistant distract the dog if it's scared. Al used to scream bloody murder; now I can do him without help. Cut after bathtime or a walk int he snow/rain; claws are much softer when they're wet. Mark it on the calendar so you can figure how often to do it. Cut often, cut little. I put them upside-down between my legs on the floor. If you don't hurt them, they'll get used to it.