Apply the oil while the clipper is running, not after you've turned it off. Switch the blade on, add a few drops along the cutting teeth, and let it run for a few seconds so the oil works its way evenly across the whole blade — including the spots you can't reach by hand. Then wipe off any excess with a clean cloth before storing. This keeps the blade lubricated all the way through, not just on the surface, and helps prevent rust and uneven wear between uses.