@Meche_03 has some really good suggestions, but a wooden door or a wooden core door where the steel sheathing does not wrap completely around the door will always be a huge point of vulnerability. You can secure your door hinges, frame and jamb all you want but unless it is a steel reinforced door with a steel (commercial) door frame, I can kick it in with one blow destroying both the door and the jamb, and separating the door from the door post.
Side doors, back doors, and garage entry doors should be steel clad solid core (preferably commercial exterior doors) and open outwards. Steel frames. Striker shields. Additional metal cladding around the knobs.
The problem is that commercial doors are expensive. Like $1000 a pop (for a pre-hung exterior door with a steel doorframe)(with hardware) kind of expensive.
What you can do is install a security gate in front of your front door. There are plenty of them out there that are strong enough to withstand a sledgehammer attack for a couple minutes, long enough for the occupants to arm themselves or at least be fully aware that someone is trying to enter.
The farther you can keep a home invader from the door itself, the better.
The security gate below is not mine, but mine is similar. Opens outward. Top lock is a dual-cylinder deadbolt (key lock on both sides, no lever to turn by hand) and the outside handle will separate from the security gate if someone pulls on it too hard to try to force it open.
(obviously you would not want to have a window right next to your door as pictured)
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