See every act you do as being of great significance. Maimonides suggests that we regard ourselves as being equally balanced between good and evil, and the world itself as similarly balanced. Therefore, one good act will tip the balance toward good in our own life and in the entire world. Conversely, one bad deed will tip the balance toward evil in our personal life and that of the entire world ("Laws of Repentance" 3:4).
For example, when someone comes to you for assistance, imagine that you are the only person who can assist this person; thus, if you help her, she will have what she needs, but if you refrain from helping, no one else will, either.
On a societal level, bad behavior tips the balance as well. Criminologists understand that if a neighborhood has many broken windows in its buildings, and they are not repaired, crime in the neighborhood, including violent crime, will soon increase; the broken windows and the unrepaired buildings become a signal to offenders that the neighborhood is a place in which disorder is accepted and crime tolerated or ignored. That is why fixing broken windows can tip the balance in the neighborhood toward better, more civil, behavior by its citizens, while ignoring such a seemingly minor detail can start a neighborhood on a path of moral deterioration.— Joseph Telushkin in A Code of Jewish Ethics: Volume 1