When you live with other people, community safety is everyone's responsibility.
DO NOT prop outside doors! Many tragedies have resulted when the wrong person slipped through a propped door.
Report the presence of strangers to residence hall staff and / or University Police. Better to be safe than sorry.
Don't let strangers into your building, even if they tell you they're there visiting a friend. Offer to call their friend for them.
Don't argue with intoxicated or drugged individuals or try to reason with them. If someone is irrational and angry, it's best to keep your voice calm and save rational conversations for later. Don't put yourself in the middle of physical danger either. Get help from an appropriate source who knows how to handle such situations.
Let someone know about "little things" such as bathroom leaks, slippery floors, broken furniture, missing screens -- your diligence will help ensure that people don't hurt themselves or have their property damaged.
If you see that a campus light is burned out or a piece of emergency equipment has been tampered with, report it right away so that it can be fixed.