Place two fingers of the opposite hand on the blade as shown to hold it firmly to the strop through each stroke. As you pull the knife in this position, tilt the back of the blade up about 12 degrees and hold it at that as best you can through the stroke. Do not let the blade roll at the end of the stroke. That will take the edge off the knife.
Lock you wrist in that position before pulling the blade to the right as shown here. Also keep your elbows locked close to you body, rotating your whole body like a machine keeping the knife locked in position through the stroke.