One of the first things you should look at is the construction of the door. How solid is it? A door that is lightweight with a hollow-core wooden construction would be easy to break so make sure it has a strong solid wood or steel core. You should also make sure the door and frame are in good condition and not showing signs of deterioration such as rotting, warping, or cracking.
What type of lock does the door have? A good quality deadbolt lock is ideal. If you want to use a chain this will be a good addition to the deadbolt but never use it instead of one. You can also install a peephole which will allow you to check who is at the door before you open it. Also, since bump keys are a popular choice for thieves these days, you may want to consider a bump-resistant lock.
Very often a front door will have glass paneling in it and, while this is aesthetically pleasing, it may make it easier for a thief to smash through. In this case, you should make sure the doors lock is positioned far enough away from the glass so that it would be difficult to reach.
Some front doors have a mail slot in the door itself. If this is the case there should be a cage or box on the inside surrounding the slot, otherwise, someone may be able to access the doors lock by way of the mail slot.
These are just some features of a secure front door. Don’t let your exterior doors become the home's security weak spot.