If anticipating a problem, go out in numbers.
Inform family/friends about your whereabouts.
Do not entertain strangers.
At night, take prepaid taxis or call known taxi stands.
If receiving regular blank or obscene calls, instal a caller-ID system.
Ask your school/college/institution to introduce self-defence classes. Enrol and do not be afraid to use your skills.
If there is crime, or even anticipation of crime, please report it to the police.