"If your nextdoor neighbour throws his trash where he's not supposed to, how can you convince him otherwise?"

Well, as general rule you could take some time to talk to your neighbors.
If your neighbor is a criminal than you are in a difficult situation- esp if the police force laughs at you if you try to discuss the issue with them. If you have a functioning law enforcement, then you try to make it clear to your neighbor that you respect laws and you don't support criminal activity- maybe the neighbor will move away. Meanwhile if neighbor is involved in serious crimes, you would report these.
If your neighbor is simply an a$$hole, then you need to find more creative solutions. For instance, you should pick up any trash in surrounding public areas, regardless of how it got there and you should make an effort to improve your area. Your future actions would depend on how your neighbor responded.