Don't flash the cash or count up the balance of your spending money in full view, same as anywhere. If walking the narrow alleys of the Red Light District keep you hand on your wallet or purse, as they are sometimes very crowded and pickpockets are always a possibility. If offered sex or drugs on the street, just say "no thank you" and move on. (I can never understand why anyone would buy sex or drugs on the street in Amsterdam.
Beware if you are a female walking around Amsterdam on your own - I was accosted every ten paces, it was a real nuisance, either they blocked my way or tapped me on the shoulder, even just saying something (usually unintelligble) became enough to put me off ever wanting to visit again. I found though that to get away from the main shopping streets and as far away from the red light district as possible diminished the harrassment.
Be careful walking alone in and around the red light district at night (stay with the crowd, I mean watch the people and stay with 'right' people), and don´t take pictures of the girls behind the windows!! (This picture is from the net!)
Walking along the canals in the evening can be hazardous to your health! Whether it be bad drivers along the barely-wide-enough pathways shared by pedestrians and vehicles, or more likely, drunk or smoked-up college students, you're bound to find yourself in the midst of a physical threat - 'mostly harmless', as the HitchHiker's Guide to the Galaxy might say, but like in any big city, you need to watch your back.
You are more likely to be bumped into & knocked down by a drunk accidently, than mugged, but always be aware.
Crowds gather in the red light district to 'window-shop' the ladies, and it's frowned upon to photograph them directly, but families and seniors will trawl side-by-side with fraternity brothers and priests (I just hope they were researching an essay on sins of the flesh!)
Keep some extra change in your pocket in case somebody holds you up ! ( try to mug you )
Don't keep to much money on you - and do not walk alone in nighttime. espescially aroung the train station and in the downtown areas. Don't fall into the canals - their toxic and bad for your health ! :)
Chances of getting mugged if not careful - stay sober , and never alone !
Any bike has a potential of being stolen - Stay away from the bikers - otherwise you migh be run down !
Don't take any major chances
After a long night out, negotiating steep, slippery slate steps is more difficult than trying to say that outloud....
Make sure you're well enough to make it home!