I'm a new DM and my ranger frequently wants to target a specific bodypart or item an enemy is holding. Stupid example, the enemy had chainmail on but no helmet and he wants to try and shoot for the face. How do you handle something like this? Is it a harder attack roll or is it ANOTHER attack roll? Do you still take AC into account?
I like to encourage them to be creative and do stuff like this so I don't just want to refuse, but at the same time I want to make it difficult enough that they aren't trying to pull it off every turn.