First measure the angle of what you have now. If you want a longer bevel, start grinding with the wheel only contacting the back of the bevel. On my oval skew, I actually prefer to grind on the side of the wheel, I don't like long hollow ground bevels. That is 100% by feel, and probably not for beginners. You have to have a confident feel, and resist the temptation to keep looking at how much you have removed. Each time you look, you have to find the bevel again. I have a flat skew with a radius cutting edge. I use a platform to work that bevel. I use a small square to transfer the point where the bevel meets the body to the other side. That way I have a guide to grind to.