1.Get to know your neighborhood aka what belongs and what doesn't...
You live in your community 24/7. Cops generally only work there. You're going to know the neighborhood better than the cops, unless you live life with blinders on.
2.If something looks real suspicious call the cops...Also make sure you have a regular telephone and not rely on your cell phone...In the case of an emergency you can punch in 9-1-1 and set it down..Your name and addy will show up on the dispatcher center incoming calls and a car will be sent..That only happens with an old fashion landline...
A few important points on phones. In my agency, I have to play dispatcher sometimes, so I know more about the 911 system than the average cop. We also have a few dispatchers here who know even more, and they may want to add to or modify this.
First, know the best way to call your local PD. 911 may go to a central dispatch for a region, while your PD may have a direct number for police dispatch. It's sometimes called a non-emergency number -- but, where I work, if you call our "non-emergency number" in a police emergency, it's ringing on OUR desk, not at the fire & rescue dispatch for the county. This'll save as much as several minutes while the 911 call taker figures out what your calling about and where you're calling from.
Second, 911 hangups and open lines. GREAT tools for self defense, because most agencies WILL send a cop to find out. If it's accidental, call back and explain right away. They may still send a cop (I generally would), but they'll be less worried when they respond.
Third, E911 is the system that advises addresses. It doesn't always work right... but it's a good tool a lot of the time. Don't rely blindly on it. Both cell and land lines are portable today; they can move with you, and sometimes the switching makes mistakes. Also, in some cases, especially in border areas of jurisdictions, it may just go to the wrong agency.
3.Alarm systems are a good deterent, but they have tendency to go off for the slightest reasons...
4. Light up your backyard..Criminals hate bright lights...If you know an electician ring your garage perimeter with flood lights..
Alarms and lights are great -- but both must in proper working order. Don't skimp the maintenance on these. And make sure that your alarm monitoring company, if you have one, has the right jurisdictional information. I once got to respond to a fire alarm just a bit outside my jurisdiction because the alarm company couldn't get it through their head that they were calling the wrong place... Fortunately, I was close, 'cause the house was on fire.
One last note on calling in a suspicious person/vehicle/whatever.
Never hesitate to do so! The dispatcher's job is to prioritize and assess the calls; they won't pull a cop from "something important" to check out your suspicious person. The most you'll do is keep that cop from writing someone a traffic ticket!