Don't attempt to clip a nail until the dog is no longer showing stress over having his legs lifted, his toes spread and manipulated. If you don't use a grooming table for nail clipping, and use your lap instead with the dog lying on its back or side, work on getting the dog comfortably in that position while you click and treat for calmness. Then pick up the clippers and hold them in the palm of your hand, and slowly touch the dog's body with the clippers. Then activate clippers while still rapidly reinforcing calm and quiet. Don't attempt to clip nails until the dog is not stressing around the presence of the clippers.
Some dogs only begin stressing once the clippers are activated.
Practice desensitizing to the sound of that sliding metal which probably indicates to a dog that something stressful is coming, or something painful. Know your dog anatomy well, and be sure you are prepared before you do an actual cut on the nail. If you cut too high, quick the dog, you'll have a much harder time gaining his confidence and are back to square one. Hold the leg with a bit of firmness, but still maintain the relaxed, flexibility of the leg. When the dog is relaxed and not fighting your touch and hold, can handle having the clippers rubbed on his body, on his legs, touching his feet, then you can begin to actually nip off a bit of nail.