1. Carry a monopod all the time.
2. No carbon-fibre ones, they shatter on impact.
3. Wear comfortable running shoes, so you can leg it quickly when trouble develops.
4. Have a flash handy, flash into your potential attacker's face to blind him/her!
(Especially useful at night!!!Remember to close your eyes when you flash)
5. Have an aerosol spray handy, repeat as above!
6. Place the police on a quick-dial button on your hp.
7. Avoid easy-to-ambush places like quiet parks, alleys, tunnels etc etc. unless of photographic interest.^^
But seriously, back while I was Taipei, I was stopped by a drunk hobo at knife-pointin He Ping Park (Peace Park coincidentally). He was kind of intoxicated, cause he was holding the knife the wrong way. So I gave him a kick in the shin, swung my 190ProB at his hands and then quickly legged it.
He was so drunk that after he fell, he just slept on the floor and didn't bother to come after me.
(Not recommended action for most people. When being mugged, it's usually better to just give the guy what he wants.)