Trim your nails once a week and use an emery board to keep the nails gently curved.
If necessary, simply use a pair of side cutter pliers and then smooth the edges with an emery board.
After three or four days of acclimating your dog to the sound of the grinder, begin using a regular emery board on his nails as the grinder is running.
Eventually, you'll be able to make the transition from the emery board to the nail grinder, but keep in mind that even after the acclimation period your dog may still not like the grinder initially.
Infected nails should be cut short and straight and carefully cleared of dead cells with an emery board.