Hide-a-key

Many homeowners, afraid they will lose their keys and lock themselves out, choose to hide a key somewhere on the property. They think they are being sneaky by placing the key under a rock, under a doormat, in a potted plant, or above the door. Burglars absolutely know about all these commonly used hiding places.

Broken Locks

Some homeowners neglect to fix broken locks right away, putting the job off for tomorrow. It is important, however, to make sure all your doors and windows have strong modern locks that are in good repair.

Burglar Alarms That Aren't Turned on

A home security system is only useful when updated and activated. Test your alarm on a regular basis and check for any upgrades to the software. And don't forget to turn it on when you leave the house, even if you're just planning to run an errand.

Untamed Landscaping

Burglars love to hide behind bushes and shrubbery; don't give them that opportunity. Keep the foliage trimmed, especially around the house, and make sure all the outdoor lights are in good working order.

Unlocked Storage Sheds

If you have a storage shed, make sure you keep it locked at all times, because otherwise you're offering thieves free use of all your tools which can certainly help them figure out a way into your home.

Keys in the Car

It's bad enough if you leave your car unlocked (you shouldn't, even in the garage), but never leave a set of house keys in the car.

Source: http://www.homesecurityinformation.com/home-security-common-mistakes.htm