What's the best self-defense?
Common sense: Don't park in dark and secluded areas. Stay in highly populated places. Be aware of what's going on around you. Pay attention to that gut feeling. Don't talk to strangers. Etc.
In particular, I like quoting Bill Cowher, former Coach of the Pittsburgh Steelers. He used to tell his players, "Nothing good happens at 1 am in a bar." He was looking to keep his players out of trouble. But this is applicable to all of us. Nothing good does happen when it's late in a (potentially) volatile location.
It's sound advice and happens to be the best self-defense - don't be in a bad place at the right time.