You could make different attack types such as Stab, Slash, Crush, etc. Each limb could have a different natural defense and weakness. For instance, arms and legs could be well protected against stabs naturally because they present a smaller target, whereas the chest or stomach might be weak to stabs. Though, the chest could be strong against slashes or crush attacks. That's presuming the enemy is not wearing armor.

Next, you could make some areas damage more than the others. The enemy would have a general pool of health, and time management would be considered in areas to attack. Say you have a mace that has excellent crush stats, and could possibly use it on the enemy's head to kill him in two hits. However, the head could be considered difficult to hit (so you would run the risk of missing). Therefore, you must decide between hitting the enemy a dozen times for low damage on another body part with the mace or take the chance of missing a few hits (and thus getting hit yourself) to critically damage the enemy with crushing attacks to the skull (where crushing attacks would be a weakness)

Then, if you got that down nicely, you could even add permanent damage (though temporary for battle) whereas stabbing someone repetitively in the chest succesfully leads to bleeding, or crushing someone's leg leads to slower move speed, or slicing someone's arm leads to slower attack speed. Pretty interesting! I hope I gave you some ideas. That's presuming you wanted content theory encouragement and not literal code.

Well you need some way to declare body parts - if the only information you need is hit points or whatever, you could simply have a few variables whose value is the hit points of that part:

leftarm = 10
rightarm = 10
head = 5
leftleg = 20
rightleg = 20
torso = 50

Of course I chose random numbers but this would make it easy to check the value to decide if the part is wounded or totally destroyed.

If you want to have more intricate control over the parts it may take some more numbers. You may want to have also a defense rating for each one, or several if you have the different attack types like someone mentioned. In that case it might be useful to have these be lists of values, such as (hp, defense, stabDef, slashDef, crushDef)

I think it would also be cool to allow individual parts to have effects on them. So, if your arm is diseased you must amputate! haha...jk...or say your arm is cursed and you can't use anything with that hand, or your legs are poisoned and so you can't walk...

So is the combat going to be turn-based, like in fallout? If not you should have some way for players to define their fighting style, like what they target most often. You could even have move combinations that you set up like macroes - for example you might have a string that goes slash arm, slash arm, stab torso, slash head, stab leg

I have thought about this kind of system and would love to see your take