Being a respectful neighbor is common decency (and the law).
Being respectful makes for a good neighborhood and community. When you live off campus, you'll need to be aware of situations like noise and crime.
Noise
As a resident it is your responsibility to manage the noise coming from your house or apartment. Local communities have laws related to noise, covering everything from parties to pets to pools.
Noise complaints are handled by different government departments depending on the source, but the first responder to a noise complaint is likely the police. In fact, the LAPD has a special noise enforcement unit specifically to respond to noise complaints in the city. You can find details about City of LA noise enforcement and rules on the LAPD website; if you live in another city be sure to check local regulations when you move in.
Incident Response
If you witness something illegal, suspicious, or dangerous in your community, don't hesitate to report it to the authorities. For an emergency, contact 911 immediately.
For other issues, contact your local police department precinct. Near campus, call the Northeast Community Police Station (323) 344-5701 and ask to speak to a watch commander; be sure to ask for disposition of call. Anywhere in the city of LA, you can also dial 311 to report nonemergency incidents. Remember to be patient - incidents may take time to resolve. This PDF flowchart will give you an idea of how a report comes in and how it is handled.