Make sure your first-aid kit contains some sort of packaged sterile cleaning pad for wiping muck out of rock- or log-given scrapes. Some of these pads are impregnated with a topical anesthetic such as lidocaine, which helps numb the area while you're rubbing and cleaning. If your pads aren't treated, make sure you add a tube of topical anesthetic (available at drug stores) to your kit. Or, if you're really macho, you can grit your teeth and suffer while cleaning the wound with plain old gauze, soap, and water.
Keep scrapes clean with lightweight cleaning pads.