An untrimmed piece of meat will be covered with long, flat nerves and a layer of fat.
Begin by removing the thicker layers of fat. The fat is attached to the nerve by a thin membrane. Slip the knife in between and cut at the membrane while pulling away the fat.
Continue to the end.
Some of the nerves are attached to the flesh by a thin membrane and are easily removed by cutting the membrane.
For thicker nerves, slip the knife in between the nerve and the flesh at one end. Holding the knife at a slight outward angle, slide it along the nerve to disengage.
Holding the loose end of the nerve, slide the knife in the other direction using a gentle sawing motion.
Depending on the cut of meat, there may be a large internal nerve. This cannot be entirely removed without splitting the piece so you want to remove the largest part. The nerve is pretty tough so you can scrape away the flesh with the tip of the knife until the nerve is exposed.