Make sure every external door has a sturdy, well-installed dead bolt lock.  Key-in-the-knob locks alone are not enough.

Sliding glass doors can offer easy access if they are not properly secured.  You can secure them by installing commercially available 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 door frame and the fixed frame.   Then insert a pin in the hole.

Lock double-hung windows with key locks or "pin" windows by drilling a small hole into a 45° angle between the inner and outer frames, then insert a nail that can be removed.  Secure basement windows with a grille or grates.

Instead of hiding keys around the outside of your home, give an extra key to a neighbor you trust.

When you move into a new house or apartment, re-key the locks.

All outside doors should be metal or solid wood.

If your doors don't fit tightly in their frames, install weather-stripping around them.

Install a peephole or wide-angle viewer in all entry doors so you can see who is outside without opening the door.  Door chains break easily and don't keep out intruders.

Thieves hate bright lights.  Install outside lights and keep them on at night.

Keep your yard clean.  Prune back shrubbery so it doesn't hide doors or windows.  Cut back tree limbs that a thief could use to climb to an upper-level window.

Clearly display your house number so police and other emergency vehicles can find your home quickly.

If you travel, create the illusion that you're at home by getting some timers that will turn lights on and off in different areas of your house throughout the evening.  Lights burning 24 hours a day signal an empty house.

Leave shades, blinds, and curtains in normal positions.  And don't let your mail pile up!  Call the post office to stop delivery or have a neighbor pick it up.

Ask local law enforcement for a free home security survey.