:imo:
Here's how I was taught, it's simple, and works perfectly;
1) With the rifle unloaded, or with a rag draped across the pan of a loaded rifle, lay the rifle on the bench pointed down range so you're standing behind the butt;
2) Bring the hammer to full cock;
3) Hold forefinger of left hand across under lower jaw to steady the hammer in place;
4) Hold a steel or brass shafted ball starter, back edge of a hunting knife, brass rod, knapping hammer, etc, etc, in the right hand;
5) Lightly tap-tap-tap-tap about 3-4-5 times across the edge of the flint to flake off tiny pieces to make a thinner sharper edge...takes very little effort and about 10 seconds.
Resume shooting...