Avoid or restrict personal contact and communication.  This doesn't mean that you tear up letters or erase messages left on your answering machine.  You'll need proof of the harassment should arrest and prosecution become necessary.

Gather evidence the moment someone's attentions begin to make you feel uncomfortable.  Keep your records in a safe deposit box or with a trusted family member or friend.

Keep a log of any sightings or contacts.  Include date, time, location, circumstances, and the names of any witnesses along with their statements.

Save all written messages, as well as the envelopes they came in.  should any unusual packages, boxes, or devices appear on the premises, leave them alone and call the police 911.

Record any threatening or inappropriate phone calls.  Note the date and time of the call.  And don't erase messages left on your answering machine.

Chronicle activities such as property damage, vandalism, and personal injury with a camera or video recorder if you can do so safely.

Call the Police 911.  If the conduct is criminal and the police are already involved, notify them of each and every incident.  Obtain copies of any legal paperwork.

Send a "Stay Away Letter" to your stalker stating that you want him/her to leave you alone.  Mail it certified so you know they received it and keep a copy to give to the police.