I am new to this as well and self taught, but from the research that I have done, it's best to scribe or mark the center line of the edge. Then take a round file at about a 45* angle to the edge on the side closest to the handle and file down to your line ( leave a little extra material). Do the same to the other side. Take a marker and color in the file slot. Now adjust your angle to the desired taper that you want and start filing again but be careful not to take off the colored in spot at the edge. This will insure you are not removing material past center line. Once you have filed down to your desired taper on both sides and still have just a smidge of marker left at edge, then you can take it to the sander using the file cut as an angle and depth guide. Grind down until you are flush with your file cut. Now you just have a little more to take to get to your center line. The extra material is for mistakes and to ensure you stay on center line with a visible line/mark. You can go ahead and take the material down to center line now or use it for your primary edge when sharpening. Hope this helps and if there is a better way some one much wiser then I can chime in.