The first DIY is to make sure all of the screws holding the plates to the door frame and door are 3" long. That's the latest standard to make it harder for someone to bust down that door with their shoulder or foot.
Those 3" long screws make it much, much harder to crack the corners of those doors or door frames to gain entry.
YOU CAN DO THIS ONE on apartment doors too. Just pre-drill the holes to be safe.