The Netherlands are a safe country, Amsterdam is even rated as one of the top 25 safest cities in the world, ...... but you should be aware of:
Several incidents on trains from Schiphol Airport to Amsterdam, where tourists have been robbed by thieves. Undercover policemen are joining this train trip now.
Fake policemen claiming to investigate creditcard fraud, showing fake identification and asking tourists to hand over creditcards and money. Travellers are advised to accompany them to the nearest police station.
Pickpockets, particulary in the center of Amsterdam, the Red Light District and at Central Station.
Fake medicines (viagra) and fake drugs are sold on the streets of the Red Light District.
Avoiding making eye contact with anyone who looks like they may be up to no good.
Using public transport, even late at night, isn't usually a problem, but in doubt take a taxi.
Locking your bike, keep valuables in a safe place, leave bags not unattended and don't leave valuables (on view) in your car.
If you are robbed, you need to go to a police station to report it. Ask for a copy for your insurance company.