On new heads use an 8" or 10" file to establish proper bevel as demonstrated in pics 1 and 2. Any time after that when sharpening the head use a good sharp 6" mill bastard file with light pressure.
Create small forward facing teeth in the edge by running the corner edge of the file along the edge as shown in pics 3 and 4. First the left blade with enough pressure to bite into the blade and then on the opposing side with very light pressure only to align the burr.
Using the flat edge of the file very lightly (only the weight of the file itself) refine the edge as shown in pics 5 and 6. You may have better results here using the wide flat side of file rather than the narrow side as shown. Repeat this step one stroke per edge and rotating until you have established the edge you want. You can also refine the edge further with a diamond stone keeping in mind that the more refined the edge the less durable it will be and the coarser the edge the more resistant to penetration it will be. Not necessary to strop this edge but I usually do every day or until the arrow has been shot and needs re-sharpening.