black nails are easiest, you just take off little slices, the nail will look grey, and when your getting close to the quick you will see a black dot apear in the middle, easier to see than white nails where your looking for a pink dot. it took me months to get good, the main key is you have to be calm and confident, if your nervous, the dog will sense it and get scared and pull and fight the clipping, making it much harder, hit a quick to many times and they may struggle everytime from the memory of the pain. it's not the size of the dog in the fight but the size of the fight in the dog, i clipped sharpe's, rotts, bulldogs, pitts, for the most part they are very easy, i would say the hardest by far are pugs, lol we had this pug named bear that came in the shop once a month, we charged the lady 20 bucks instead of 8 because it took two people to hold him down and a third to clip him, and we still all ended up covered in scratches by the time it was done.