UMass is not strict by any means, and getting in deep trouble here is like getting a bad grade in a really easy class—you have to try. However, certain behavior will get you in trouble if you get caught. The penalties for doing something serious are severe, but if you get caught with a beer in your room, you might just have to go to an alcohol education class. However, if you do it again, the punishment stiffens. But, really, UMass authorities, including the RAs, are good about focusing on what's important—safety. Typically, three offenses are the most leeway you will have, and after that, housing probation becomes an option. It is commonly known as being "written up" when an RA catches you smoking, possessing alcohol, or even having lighters or candles. Basically, think wisely about how visible you keep your possessions. RAs cannot enter your room without permission.
One thing RAs do crack the whip about is playing with the fire extinguishers that are located on each floor, so don't do that. Another thing that is taken seriously on campus is stopping your car for pedestrians, a law that doesn't necessarily apply to people driving around off campus in Amherst. The fines are steep for neglecting this law, and it is not taken lightly. Unfortunately, during specific times of the day, like when classes are getting out, this means you may have to sit at a crosswalk for a long time to allow everyone to cross. When leaving campus, don't assume that the behavior you can get away with on campus won't get you in trouble off—the Amherst Police don't tolerate college students as much as the UMass Police.