Gravers are sold in their hardened state and any grinding should be done in such a way that this temper is preserved. Touch the tool lightly to the grinding wheel, dipping it frequently into water throughout the process to prevent it from overheating. If the steel starts to show color the temper has been compromised.
The first step is to narrow the area adjacent to the tip for 1-2 centimeters (1/2 - 3/4 inch). This will allow better viewing of the working tip of the tool and facilitate sharpening since there is less metal to be removed. Use a stone to cut away at least half of the top section at the tip, creating a gentle arc as shown. This edge should be made smooth because your fingers will be resting on it while cutting. Do not go too far back because this will weaken the tool.
The belly or underside of the graver is ground so it shows two symmetrical facets. If the tool was turned over, these might be said to resemble the roof of a house. The angle between these two facets will be between 30 and 60° depending upon the hardness of the material to be cut. A narrow tip cuts a finer line but is more fragile.
The face of the tool is then ground to a slope, typically around 45°, again depending on the material being cut; the finer the slope, the more delicate the tool. It might help to visualize a pencil point. If it is made very long and pointy it makes a fine line but often breaks in use.
Both belly and face surfaces should be perfectly flat like the facets on a gem. This will insure that the angles where the faces meet are straight and crisp, which in turn is what makes the tool sharp. Grinding is usually done on an oilstone, working in a circular stroke, first on a coarse stone and then on a finer one. When the surfaces are correct - check with magnification - shift to a polishing stone like Arkansas or a fine abrasive paper. Follow this with a few strokes on a hard leather with a polishing powder to create a mirror bright finish.
Test the sharpening by sliding the tip of the graver along your thumb nail. A properly sharpened tool will stick immediately while an improperly shaped tool will slide off. There is no point in going to the metal until the tool passes this test. Cutting with a dull graver is tedious, uncontrolled and almost certain to ruin the work.