My friend has cholera. How do I avoid getting it?

Avoid their stool. Cholera is transmitted by the fecal-oral route, either by contaminated water or food. In the usa there is very little chance to acquire cholera. Where had your friend been. Stay away from their stools, wash your hands and watch what you eat and drink carefully.
It's food contamintn. Cholera infects through fecal oral route. Means wash hands thoroughly, and food need not to be contaminated by the hand of the patients that may carry the bacteria from the diarrhea.