I grew up in Miami, which isn't the safest of cities, and lived before that in Detroit, though granted, on the outskirts.

Situational awareness is key. Walk with confidence. Have keys in your hand, pointing out through your clenched fingers, especially if you feel threatened. Palm up and up into the nose if you encounter an assailant. If you are wearing heels, stepping on his instep may also help, but the nose is an easier target. Then throw something (anything not valuable) away to one side, and run to the other side. No matter what you throw, he'll likely go after it. I have also learned how to whistle ear-shatteringly loud with my fingers, in case I need to call attention to myself. As in, anyone nearby has pain, loud.