So you might have just been broken into, or are proactively seeking advice on how to prevent unwanted access. The most common criminal method of gaining entry is to damage the lock or door to bypass the locking system. Rarely do they know how to pick/manipulate locks with enough skill to be effective.
You can choose to have a qualified and experienced locksmith install the right types of locks which will certainly slow them down if not completely stop them, but there are also types of door hardware that can be effective when installed correctly. A blocker plate, sometimes called a latch guard, is perhaps the simplest way to make a criminal think twice about attempting entry on the door. The latch is often exposed enough so that a crow bar or similar tool can be used to force the lock open. See the difference a blocker plate makes below.