The way you never get attacked on the streets downtown at 2 AM is very simple ~ pretty much follow the specifics Derbyshire advised, but also ~ most important one is NEVER let anyone get within 100 yards of you and never advance on your objective (whether it's crossing the street or getting to your car) unless you know of at least TWO ways to escape from wherever you are at.
Just drop the black stuff ~ all of it applies to human beings you don't know, or maybe you do know them.
Oh, yeah, TIE YOUR SHOES BEFORE VENTURING OUT ON THE STREETS. Nothing like starting to run and losing a shoe.
MInor piece of advice ~ you encounter a guy at night during late business hours and he's begging for change ~ 'jus a dollah man' ~ DO NOT pull your wallet, and don't even put a hand in your pants pocket. He and his buddy you didn't see will have you on the ground in a sec.
Beggars don't do nights. Criminals do.