Change the lock at your new rent or bought house or premises, as you never really know who has the keys.
When you need a lock, pick a high security model with fitting rod system, so there is not gap between the frame and the door and so it is much more difficult entering into the dwelling. If the lock cylinder is Europe type -which are shaped as shown bellow- install an anti-breaking cylinder, as this type of cylinders are very weak and thieves know that and are used to enter relatively quickly and quietly.
When you are at home, double-lock and leave the keys in a visible place near the door. This makes impossible the entry into the housing through credit cards or x-ray photographs. Thus you will be safe and yet quickly find the key in case of need to leave in a hurry, fire, etc.
Do not open the doorway to anyone who asks on the entry phone, so you prevent further shocks.
When you use the exit or entrance door to the grounds or parking, make sure it is securely closed, because the elapse of time and poor maintenance result in door closers and floor springs losing their closing force.
When leaving home, you must always lock one or double-lock, never just rush out. This makes impossible entering into the housing through credit cards or x-ray photographs which are used to reverse the bolting mechanism.