Keep your doors locked at all times, even when you are at home, and remember to close and lock your windows when you leave, even if it's just to walk the dog.
Install new locks or have the tumblers reset when you move into a previously occupied building.
Install auxiliary dead bolt locks with 1-inch throw on all exterior doors and use them. A second lock is often the easiest and sometimes the cheapest way of strengthening the security of an entrance door.
Keep the number of keys to a minimum by having all the locks keyed the same.
Doors with glass panes should be fitted with double-cylinder locks, requiring keys both inside and out. Keep a key near the door in a location known by all occupants so they can exit in case of fire or other emergency.
Sliding glass doors should lock from the inside. A strip of wood placed in the inside bottom track will prevent its opening. Commercial "locking bars" or patio door locks are also available.
Secure all entrances - including garage doors, basement doors and windows, sun decks, and porch doors - day and night. Don't hide keys outside.
Keep your keys to yourself. Don't entrust them to tradesmen, maids, repairmen, etc. Separate house keys from car keys when leaving your car with parking lot attendants.
If someone forces open your door, leave immediately by a different door and go to a neighbor's house to call police.
Don't open your door to strangers. When someone is outside your door and you don't know who it is, keep the door shut, even if you have a security chain. Talk to the caller through the door or a nearby window. You may wish to install a peephole or, even better, a door-mounted viewing lens.
When working in the yard, garage, basement or upstairs, keep your doors locked.