Your front door is your first line of defence, it is therefore important to use a good quality cylinder or 5 Lever mortise lock in conjunction with an additional security device such as a deadbolt or nightlatch.

Replace hollow core external doors with solid wood, fiberglass or metal and make sure that hinges are on the inside of the door to prevent potential intruders from removing the pins and pulling the door out of the frame.  

External doors should have only key operated locks so that if a burglar should gain entry through a window, he will have to also exit that way.