Lay a three-tab asphalt shingle on a flat wooden surface. Lay it down so that the smooth side faces upward and the tabs face away from you.
Place a utility knife blade in between one of the slots in the tabs. Cut down from the slot at a left 70-degree angle until you reach the edge of the shingle. Set the knife back in the slot and cut down from the slot at a right 70-degree angle. Repeat this process in the second slot between the shingle tabs. When finished, you'll have three individual roof ridge shingles. One of them will be tapered on both sides and the other two will only be tapered on one side.
Cut the sides of both shingles that need to be tapered. Make a 70-degree angled cut from the center line out to the edge of the shingle. The cuts need to be made in the opposite direction of the tab side of the shingles. You should now have three tapered ridge shingles ready for installation.