I just got my bike stolen in the Netherlands, so maybe I'm not the best person to answer this, but nevertheless, let me try:
Overal infrastructure and cleanliness; everything is well maintained and you can get everywhere with ease. This makes that most people feel uncomfortable doing criminal things. (Except for bike thiefs; to profit the infra you need a bike ;))
Good social security; it has been measured that in the Dutch system it's pretty hard to be really poor. Most crimes result from necessity, so solving the problem of people being poor helps the crime rate down. (That's one of the reasons why I advocate a Basic Income)
Trying to solve the root problem instead of removing the sympthoms; for example drug usage is initially not seen as a crime but as a personal problem, and you can get help for it usually without risking to be arrested. (Yes, drugs are neither legal nor decriminalized in the Netherlands, they are tolerated so we can help those having problems with it.)
Accomodating possible criminal minds in a place where they work best; we have a lot of ICT and Security jobs, places where potential criminals are right at home without actually being in the criminal circuit.
I would like to hear if I am wrong about something or if I missed something important.