Ghouls are among the most common enemies you will face in the Fallout 4's wasteland. Here's a quick guide describing how you can take them down taking the less amount of risks possible. First, take in mind it's a matter of shooting or cutting their limbs off to make the highest degree of damage.
So aim for the legs first, so you can prevent them from moving or even running towards you and starting to make some several damage, especially from radiations which are pretty annoying.
Aim for the head only when you are 1v1, never in 2v2 +, just because doing that will make you lose some precious seconds and they will take advantage of that running towards you and providing you radiation points and lowering your health.
Overall, for every enemy you meet remember Fallout 4 is a game where tactics really matter. You should just approach it the way you do with Dark Souls rather than Call of Duty, simply because running in front of your enemy isn't always (it's almost never, actually) the best solution for you to clear an area. Try the stealth way, too, it's really enjoyable.