Never leave a house key available under a doormat, in a flower pot, on the ledge of the door. Sliding glass doors and windows can offer easy access if they are not properly secured. You can bolster them by installing additional security locks or putting a broomstick or dowel in the inside track to jam the door. To prevent the door being lifted off the track, drill a hole through the sliding glass door frame and the fixed frame - then insert a pin in the hole. Security locks should be added to garage, patio or other doors that lead into the home.
Thieves hate bright lights.
Install exterior lights on timers that illuminate your doors and windows all through the night. Prune back your shrubbery so it doesn't hide doors and windows. Cut back any tree limbs that a burglar could use to climb to an upper-level window. Stop mail and newspaper delivery if you are going to be away for an extended period of time. Consider an alarm system or owning a dog for added protection.